static, plain vs dynamic, interactive
A web application is like an "application in the web"
so you're probably interested in developing web apps...
example of using vanilla JS: https://codesandbox.io/s/react-workshop-js-dom-manipulations-js95u
so you're probably wondering why React, of all libraries...
We'll be using React as our library but a lot of the things you learn here are also general concepts in web UI development, and applicable in vanilla JS and other frontend libraries/frameworks.