They have tutorials, reference materials, and also a ‘try it now’ feature for most things, which gives you a sandbox that you can experiment with the code and see what the effect is of any changes you make.
A good place to run small experiments and learn how things work is jsfiddle. You get four panes in the screen: the HTML which is the content, the CSS which describes the presentation, and the JavaScript which is the machinery for the moving parts:
You can also build a small static site for free on GitHub (but you do have to sign up) which you can make public. Here’s an example extremely simple site: https://biged.github.io/Simple-website/
perhaps a bit more advanced, see codepen.io
which is, like jsfiddle, a site to try out the machinery behind a web page, but also a place to find and share techniques with other users.
This tool got mentioned the other day - it’s a great tool for pulling in mock data from an API into a web page (or other app) over HTTP (there are some example structures on their hosted version, with the option set up limited custom objects):
What’s even better: you can run a local version of Json Placeholder (or host your own) to mock whatever ReST API you need - just install it via npm & fire it up with a json file as a database (means you can use whatever schema you like) - allows updates etc. just like the hosted version.