Most of the three.js projects we see involve real-time 3D graphics which includes interactions of the users. For doing these 3D animations math is required, Three.js comes with its own math library which consists of specific classes for 3D math.
If you have Node.js and NPM set up on your computer you can easily import this by typing a command in your command prompt: npm i three
And if you prefer YARN over NPM you can type: yarn add three
You can, of course, build a game engine and use three for rendering, and for building blocks of the engine. Online IDE’s with built-in support for Three.js is available on the Internet.