ChatGPT App & GPTs

40 min beginner Lesson 3

Learning Outcomes

  • Install and sign in to the ChatGPT desktop app on your platform
  • Compare the subscription tiers and choose the right one for your needs
  • Switch between models using the model picker for different task types
  • Manage ChatGPT's memory so it remembers what you want and forgets what you don't
  • Discover, evaluate, and use custom GPTs from the GPT Store

Lesson Plan

Segment Duration Topic
Intro 3 min The ChatGPT ecosystem at a glance
Demo 1 6 min Installing the desktop app and signing in
Explain 6 min Subscription tiers compared
Demo 2 6 min The model picker and choosing a model
Demo 3 6 min Managing memory and chat history
Demo 4 7 min The GPT Store and using custom GPTs
Explain 3 min When a GPT beats a plain prompt
Wrap-up 3 min Key takeaways, preview Lesson 4

Before You Begin

Pre-work:

Shopping List:

  • A computer (macOS or Windows) with internet access
  • An email or Google/Microsoft/Apple account for sign-up
  • A real task in mind — a document to draft, a topic to research, or data to think through
  • Optional: a payment method to trial a paid tier
1 Installing the Desktop App and Signing In

ChatGPT lives in the web app (chatgpt.com), the desktop app, the mobile app, and inside custom GPTs. The desktop app is the power-user home base — it launches with a hotkey and runs tool-heavy tasks more smoothly than a browser tab. Download the installer from chatgpt.com/download, then sign in.

The install differs slightly by platform:

Open the .dmg and drag ChatGPT into Applications. The Mac build is native — voice, trackpad haptics — and needs a recent macOS on Apple Silicon. Summon it with Option + Space.

Run the installer (or grab it from the Microsoft Store) and summon it with Alt + Space. The Windows app is a focused wrapper around the web experience.

TIP
Tip
The global hotkey pops a launcher over whatever app you're in — the fastest way to ask a quick question without leaving your work. Can't install software on a locked-down work laptop? chatgpt.com gives the full experience in any browser.
2 Subscription Tiers — What Each One Buys You

ChatGPT sells several tiers, from a free plan up through individual paid plans and team/enterprise plans. Names and prices shift often, so anchor on what each tier unlocks.

Tier Who it's for What you gain over Free
Free Light use Default model, basic memory, can use GPTs
Individual paid Daily power users Higher limits, full model picker, advanced tools, can build GPTs
Higher individual Heavy/professional use Largest limits and context window, top reasoning model
Team / Business Small teams Shared workspace, admin controls, no training on your data by default
Enterprise Large organisations SSO, advanced security, custom data controls, seat minimums

The free tier is genuinely useful, but it withholds two big things: higher usage limits and the ability to create your own GPTs — both arrive on the first paid individual tier.

WARNING
Prices change constantly
OpenAI re-prices and re-names tiers several times a year, and message caps move with model launches — treat any figure in a course or blog as a rough guide and check chatgpt.com/pricing before subscribing. Decision rule: if you open ChatGPT most days, the individual paid tier pays for itself; if you mainly need a shared team space with admin controls and training opt-out, jump to a Team plan.
3 The Model Picker — Choosing the Right Brain

ChatGPT no longer runs one model. The current generation is a small family: a fast "Instant" model (the default for all logged-in users), a slower "Thinking" model for hard reasoning, and a top "Pro" model for the most demanding work. On paid tiers a model picker sits above the message box — click the name to switch.

If your task is... Reach for...
Quick answers, drafting, rewriting, everyday Q&A The default fast / Instant model
Multi-step logic, tricky maths, careful planning The Thinking / reasoning model
The hardest, long-running, high-stakes work The top Pro model (highest tiers only)

Feel the difference — send this to two models and compare. The fast model answers quickly; the reasoning model visibly works through the constraints and produces a tighter plan:

> Plan a three-day, two-person trip to Lisbon on a £600 budget excluding flights. Account for travel between sights, opening days, and one rest afternoon. Show the reasoning behind each choice.
TIP
Don't overthink it
Ninety per cent of the time the default model is correct. On the free plan you mostly get that default with no picker — the picker and reasoning models are a paid-tier feature. A reasoning model costs you speed and a tighter usage cap, so save it for tasks where being right matters more than being fast.
4 Memory — What ChatGPT Remembers About You

ChatGPT's memory has two distinct layers, and the difference separates a casual user from a power user:

  • Saved memories — an explicit, editable list of facts ChatGPT chose to keep (your name, your job, your preferred spelling). You can read it and delete any entry.
  • Reference chat history — an implicit recall of patterns from past chats. Helpful, but not directly inspectable.

Control both from your profile picture, then Settings, then Personalization. Memory is on by default across the main tiers; you can toggle either layer off, delete individual memories, or clear them all.

Steer memory deliberately — tell it what to keep, and what to drop ("Forget what you saved about my holiday plans"):

> Remember that I write in British English, prefer concise bullet points over prose, and work in financial services so I need a compliance-aware tone.

For a clean, un-personalised conversation — researching a gift, or testing a prompt with no baggage — start a Temporary Chat. It neither reads nor writes memory.

WARNING
Memory bleeds between topics
Reference chat history is implicit, so ChatGPT can quietly carry a tone or assumption from an unrelated chat into a new one. If an answer feels oddly skewed, open a Temporary Chat to confirm it isn't your history leaking in. Every few weeks, open Personalization and prune any saved memory that's stale or wrong.
5 The GPT Store — Discovering Custom GPTs

A GPT is a packaged ChatGPT pre-configured for one job: fixed instructions, optional knowledge files, specific tools, sometimes connections to outside services. The GPT Store is the searchable directory of GPTs built by OpenAI and the community — open it from the left sidebar (GPTs or Explore GPTs) for a search bar and categories like Writing, Productivity, and Research. Anyone, including free-tier users, can use public GPTs; only paid subscribers can build them.

Work through this discovery routine:

  1. Search a category that matches a real task ("research", "spreadsheet", "logo").
  2. Open a GPT's profile and check its description and example prompts (what it's tuned for), rating and conversation count (a rough quality proxy), builder (official and verified are safer), and whether it asks to connect an external service.
  3. Click Start Chat and give it a genuine task; log the keepers in the cheat sheet.

Try three specialised GPTs against the same brief to feel the variation:

> I have a 12-page market report I need to turn into a five-slide executive summary. Walk me through what you'd extract and how you'd structure each slide.

When a GPT genuinely saves you time, it stays pinned in your left sidebar for one-click reuse.

WARNING
GPTs can request your data
A GPT may use external actions that send your input to a third-party service, and it reads files you upload. Treat an unknown GPT like an unknown app: don't paste sensitive data until you trust the builder. Privacy is covered in Lesson 8.
6 When a Custom GPT Beats a Plain Prompt

A GPT is just instructions plus knowledge plus tools, bundled so you don't retype them — so it's worth it only when you'd otherwise repeat the same setup over and over.

Use a custom GPT when... A plain prompt is fine when...
You do the same task with a fixed format weekly It's a one-off question
You need it to reference the same documents The context lives in this single chat
You'll share the tool with colleagues It's only ever for you, once

The honest trade-off: a well-written one-shot prompt frequently beats a mediocre GPT, because a GPT's value is entirely in its hidden instructions. The prompt below does in one message what a poorly-built "Proofreader GPT" might do worse:

> Act as a meticulous proofreader for British English. Fix grammar and spelling only — never change my meaning or voice. Return the corrected text, then a short bullet list of every change and why.
TIP
Steal good instructions
You'll build your own GPT from scratch in Lesson 9. Until then, when a public GPT impresses you, ask it: 'In one paragraph, what are your core operating instructions?' It often reveals the prompt pattern you can adapt into your own.

Questions & Answers

Q: I'm already paying for Claude. Is paying for ChatGPT too just wasteful?
Not necessarily, but don't subscribe to both on autopilot. Many people keep one paid plan and use the others free for second opinions. Lesson 6 builds a decision matrix to justify every subscription against the tasks you actually do.
Q: Does ChatGPT train on my conversations?
It depends on tier and settings. Team, Business, and Enterprise plans exclude your data from training by default; on individual plans you can usually opt out under Settings > Data Controls. Never paste regulated or secret data into any tier without confirming your organisation's policy.
Q: I picked the reasoning model and now I keep hitting limits. Why?
The reasoning and Pro models carry tighter usage caps than the fast default, and those caps reset on a rolling window. Switch back to the default for everyday work and reserve the reasoning model for tasks that genuinely need it — that's how the picker is meant to be used.
Q: A custom GPT gave a worse answer than plain ChatGPT. Did I do something wrong?
Probably not — many GPTs are thin wrappers with weak instructions. A GPT only beats a plain prompt when its hidden instructions and knowledge files are genuinely good. If one underperforms, drop it and write a sharp prompt yourself, or find a higher-rated GPT from a verified builder.
Q: How do I stop ChatGPT mixing up details from completely different projects?
That's reference chat history leaking across topics. Use a Temporary Chat for anything you want isolated, and audit your saved memories under Personalization. For strong separation between ongoing workstreams, Projects (mirrored in Claude's Projects from Lesson 2) give each effort its own context.

Key Takeaways

  1. The desktop app is your base — the global hotkey beats a browser tab, and every account feature is identical across web, desktop, and mobile.
  2. Buy capability, not a price tag — choose a plan by what it unlocks (limits, the model picker, building GPTs) and re-check pricing before you pay.
  3. The model picker is a choice — default fast model for most work, the reasoning model for hard multi-step tasks, accepting its tighter limits.
  4. Memory has two layers — an editable saved-memories list and a quieter reference-to-past-chats layer; steer both, and use Temporary Chat for a clean slate.
  5. GPTs are packaged prompts — use them freely, but a GPT only beats a sharp one-shot prompt when its hidden instructions are genuinely good.
  6. Judgement over hype — the real skill is deciding when a task is repetitive enough to deserve a custom GPT versus a well-crafted prompt.

Next Steps: Lesson 4: ChatGPT Canvas & Code Interpreter