What is HTTP and what are the most common HTTP methods?

HTTP is the language browsers and servers use to talk to each other — like a standardised postal system for the web. Each HTTP method is like a type of request letter: GET says 'please send me this', POST says 'I'm sending you something new to store', PUT says 'replace this file with what I'm sending', PATCH says 'update just this part', and DELETE says 'throw this away'. The server always writes back with a status code — 200 means 'done', 404 means 'couldn't find it', 500 means 'I broke'.