Addresses: IP · Domain · DNS · Port
IP is a computer's numeric address on the network (140.82.121.4); a domain is its human-readable name (github.com); DNS is the "directory" that turns a name into an IP; a port is a specific "door" on that same machine (443, 8080). Why: without an address, lesson 1's request never arrives. You already hit ports today (localhost:8080, the Supabase URL), and in Phase 13 you'll attach a domain to your own server. When: writing a server URL, at the "port already in use" error, diagnosing "the site won't open," reaching a PC's backend from a phone. How: you type github.com → the OS asks DNS → DNS returns an IP → the request goes to that IP's specific port. Where: every network connection — browser to website, your APK to Supabase, PC to phone (wireless debugging is IP + port too). Who: developers every day; DevOps when configuring domains/DNS.