What is a backend and a REST API, explained simply

When you open your banking app and see your balance, the app doesn't store that number: it asks a server for it. That server, with its logic and database, is the backend.

Frontend vs. backend

• Frontend: what you see and touch (screens, buttons, forms).
• Backend: what happens behind the scenes (checking your password, computing your balance, saving a transfer).

An analogy: in a restaurant, the frontend is the waiter and the menu; the backend is the kitchen.

What is an API?

An API is the agreement on how the frontend asks the backend for things. In a REST API every resource has an address (URL) and uses HTTP verbs:

Verb	Purpose	Example
GET	Read	GET /accounts/123 → your balance
POST	Create	POST /transfers → a new transfer
PUT / PATCH	Update	PATCH /users/5 → change your email
DELETE	Delete	DELETE /cards/9 → cancel a card

The backend replies with data (usually JSON) and a status code: 200 all good, 404 not found, 401 not signed in, 500 server error.

What to learn as a junior backend developer

1. A language: TypeScript with Node.js is a great entry point (Java, Python or Go work too).
2. HTTP and REST: verbs, status codes, headers.
3. A database: SQL (PostgreSQL) and how to connect to it from code.
4. Validation and security: never trust what comes from the user.
5. Testing: automated tests so you don't break what already works.
6. Deployment: publishing your API to the cloud.

Your first project

A to-do API with user accounts: create, list, complete and delete tasks, and each user sees only their own. It looks simple but touches everything important.

Next step

Codea's free Backend Developer Jr route takes you from zero to a real API with a database, tests and deployment in 6 weeks. Route content is in Spanish.