There are multiple ways to start using React.js library. Although, the most convenient one is by using Babel+Webpack.
React uses JSX syntax. Babel is a transpiler i.e. it converts the JSX to vanilla JavaScript. You can view babel as an intermediate step between your code and "executable" code.
React also uses ES6, which is not supported by most of the browsers. Babel converts the ES6 code to a code which is compatible with the browsers.
The best combination for a mature React project would be React+babel+Webpack. In order to run babel and webpack, you'll need node.
I'd suggest you to take a tutorial first to get your hands dirty.
