These three tools are usually grouped together because they are all necessary to build interesting websites, but each one totally unique.
- Manipulate the DOM in your browser
- Send and receive HTTP requests
- Perform asynchronous operations
- Offload work to 3rd party services
You'll learn more about all these features later on in this bootcamp. For now you'll just have to worry about the basics (functions, variables, control flow), and a little bit of DOM manipulation.
CSS isn't quite a Markup Language, and isn't quite a programming language. But it can be used to many of the same things as JS or HTML. CSS is it's own strange beast, some love it and some hate it.