Software, zoomed out

In Level 0 you learned that a program is a file full of instructions, and running it makes a copy come alive in memory. That’s it. That’s the whole idea.

Now zoom out. Spotify, your bank’s website, the app that delivered your food, the thing you’re reading this on, Claude itself — every single one of them is the same idea at a bigger scale.

Software is just programs running on computers. There is no magic layer underneath.

This level is a vocabulary tour. By the end of it, when Claude says “this is a React app with a Postgres database talking to a Stripe API,” you’ll know what every word in that sentence means.

Why this matters before Level 4

In Level 4 you’re going to open a real codebase with Claude and ask it questions. The answers are going to be full of words like frontend, server, API, endpoint, database, dependency, deploy.

You can’t ask good questions about a world you don’t have words for. So before we point Claude at a real project, we spend one level filling in the vocabulary.

No code, no commands. Just a map.

What you’ll learn this level

The headlines, in order:

• A piece of software is usually made of two halves — one you see (frontend), one you don’t (backend).
• Those halves talk to each other in a specific pattern called client and server.
• They talk over the internet, using URLs as addresses.
• The messages they send each other are shaped by an API — a contract.
• Most software has to remember things between visits, and that’s what a database is for.
• The actual instructions for all of this live in a codebase, also called a repo.
• Repos are built using languages, frameworks, and packages — three different words for “code you write” vs “code you use.”
• And finally: code can run on your laptop or somewhere else, and the difference matters.

That’s nine lessons. None of them have homework. All of them are short.

A note for the experienced reader

If you’ve shipped a web app, you can skim this level — read the bold words, ignore the rest. The lessons exist mostly to keep the non-technical reader oriented before Level 4. We’ll be back to your speed soon.

What’s next

Start with the split that explains almost everything else: the part of software you see, and the part you don’t.