React simplifies complex tasks by treating each section of a webpage separately. One of React’s library features is that you can decide to apply it to a specific element in a DOM without affecting how others work. However, since React is scalable, you can also use it to build the whole website.
So, the fact that you can use small parts of React in your app components means you can use it as a library. But, you can also use it as a framework when your whole app depends on it for responsiveness.
React has two technologies: Reactjs and React Native. Although these two technologies have little differences, using React Native is easy once you’re a master of Reactjs. However, React Native comes in handy for building mobile apps
To get a better hold of React, you can check out its documentation at reactjs.org.