Representational State Transfer. It's a set of rules for how computers talk to each other over the web. It treats everything as a Resource (a noun) that you can act upon using Verbs.
You (Client): You are hungry. You look at the Menu (Documentation).
Waiter (API): Takes your order to the kitchen. You don't know how the kitchen works; you just talk to the waiter.
Kitchen (Server/DB): Cooks the food (Data) and gives it back to the waiter.
Retrieve data.
Like reading a blog post or viewing a profile. Safe to run multiple times (Idempotent).
Create data.
Like submitting a signup form. Adds a new entry to the database.
Update data.
PUT replaces the whole object. PATCH just updates one field (like changing your password).
Remove data.
Like deleting a photo. It's gone forever.
Mission: You are the Client. Interact with the "Users" database.
Try: GET to see all, POST to add yourself, or DELETE user #1.