The big picture

Almost every app you'll build is made of four parts that talk to each other:

• Frontend — what the user sees and clicks. The screens, buttons, and text inside a browser or phone app.
• Backend — the logic that runs on a server you control. It enforces the rules, does the work, and decides who's allowed to do what.
• Database — where information lives so it's still there tomorrow. Accounts, posts, orders.
• Hosting — the computers, somewhere out in the world, that actually run all of the above so other people can reach it.

Here's how they connect:

   ┌──────────────┐        request         ┌──────────────┐        query        ┌──────────────┐
   │              │ ─────────────────────▶ │              │ ──────────────────▶ │              │
   │   FRONTEND   │                        │   BACKEND    │                     │   DATABASE   │
   │  (browser)   │ ◀───────────────────── │  (server)    │ ◀────────────────── │  (storage)   │
   │              │       response         │              │        rows         │              │
   └──────────────┘                        └──────────────┘                     └──────────────┘
        what you see                       the rules + logic                    where data lives
   └──────────────────────────── all of this runs on HOSTING ───────────────────────────────────┘

The frontend never talks to the database directly. It always goes through the backend, where the rules live. That single fact explains a lot about how apps are built — and why "just let the page read the database" is almost never the answer.