VSC includes many out-of-the-box features, with which you can actually get started and working with no problems. By means of extensions, you can add support for languages, debugging, code quality, and many more functions. Configuring visual aspects is also provided, and you can change VSC's theme, shortcuts, and general preferences. However, you will want to add even more functionality to VSC, and that's where extensions (plugins) come in.
You can even develop your own extensions for VSC, though we won't be getting into that subject in this book. If you are interested, check out https://code.visualstudio.com/docs/extensions/overview. Extensions can be written in either JS or TypeScript (see the Adding Flow for data types checks section), and of course you can develop them by using VSC itself!