Pick what you're trying to build — a form that posts to a webhook, a grid, a Python API call — answer a few questions, and get working code with every line explained. Then look up the attribute you half-remember, or paste in an error and be told what it means.
Almost all of this runs in your browser. The one exception is fetching a page you paste a link to — a browser is not allowed to read another site's HTML, so that request goes through this site's server. The URL is all that is sent, and nothing about it is stored.