How do I vibe code an app or website with AI, step by step?

Pick one app builder, describe one small app, and improve it one change at a time. 1) Write half a page: who it is for, the three things it must do, and what it should not do yet. 2) Start free: Lovable gives 5 build credits a day and free chat for planning, Replit's Free Mode builds from a prompt, and Bolt is free with daily limits. 3) Ask the builder to question you first, then send a first prompt with the outcome and how you will know it works. 4) Test in the preview and ask for one fix or feature per message; go back to an earlier version when something breaks. 5) Add sign-in and a database through the builder's own backend, and keep keys in its secrets, never in a prompt. 6) Publish to the free address, then move to a paid plan for your own domain (Bolt Pro is $25 a month, Replit Core $20). 7) Connect GitHub so the code is yours. If you already code, the same loop works in Claude Code or Codex.