The web stack in plain English
Browser, server, database — the three-place model that makes every later decision make sense, and why this course uses Next.js for all of it.
Every web app — Gmail, your bank, Replyable — is the same three places having a conversation. Hold this model and nothing in the course will feel arbitrary:
- The browser (frontend) — runs on the user's device, draws the screens, reacts to clicks. Code here is visible to anyone who presses F12 (Cmd-Option-I on a Mac), which is why nothing secret ever lives in it. Languages of the realm: HTML (structure), CSS (appearance), JavaScript (behavior) — your assistant writes all three; you learn to recognize which is which.
- The server (backend) — runs on a computer you control (well — rent), holds the secrets (API keys, passwords-hashing, business rules), and is the only place allowed to talk to the database and the AI. When the browser needs something done, it asks the server via an API — a doorbell with a defined question and a defined answer shape.
- The database — the filing cabinet that survives restarts. Tables of rows, like spreadsheets with rules. Replyable's database: a
messagestable and arepliestable. Everything users create lives here; everything else is decoration around it.
Why Next.js (and why one framework, not a tour)
Next.js is a framework — pre-made structure — that lets one project contain all three places: pages for the browser, server code for the secrets, and easy database wiring. It's built on React (the dominant way to build interfaces, out of reusable pieces called components) and it deploys to production in minutes. We teach one stack rather than surveying five because beginners drown in choice, assistants generate excellent Next.js (it's the best-trodden path in their training data), and — this matters — the marketing site of the very company whose course you're reading is a Next.js app. It's the industry default for a reason, and defaults are a gift when you're new.
For the whole course, when anything is confusing, ask: 'which of the three places does this live in?' Styling issue → browser. Key not working → server. Data vanished on refresh → database (or the absence of one). The assistant answers this question beautifully when asked directly — 'is this frontend or backend, and why?' — and each answer strengthens the map that makes you the editor rather than the passenger.