I am learning to code in React, a JavaScript language for web development.
Yes; ReactJS is a popular Java Script to learn.  Facebook and Instagram use this style of Java Script.  What are you thinking that you might do with such skills?
I want to start my own social media website. I want to innovate and introduce new features.
Then you are heading down the right track.  React processes user interfaces only!  So, a social media website would be perfect.  Do you have a name yet for your site, or is that top secret?
Still on the drawing board for that. Maybe something like Snapbook.
Just a little history for you.  ReactJS was first deployed on Facebook in 2011.  Later, Instagram picked it up in 2012.  It was finally open-sourced in the US in May of 2013.  So, it is definitely available for you.  Do you think you'll have a pay site, or will yours be free too?
It will definitely be free to use with targeted ads eventually bringing in the revenue.
Like I said, it sounds like you are on the right track.  On April 18, 2017, Facebook announced React Fiber.  Its a newer algorithm.  In fact, all future framework will be used under the development of the React Fiber framework.  Keep it up, my friend.