ReactJS, the library, is very simple to get started with. However there are a few other parts to learning React, I have tried to break it down here. I hope you will find it useful.
Once you are done with these, You can read the official getting started page and then their tutorial using starter kit.
The tutorial is good enough to give you a good sense of what React is all about and how it is actually used then you can look into best practices of React.
Frontend tooling is not specific to React but its definitely a considerable part of building a real world project in React. so understanding dependency management and build systems are crucial. There are plenty of options out there and most of them are unstable which makes frontend tooling really complex and confusing.
This tiny book explains popular choices and a series of posts by Tyler McGinnis uses gulp and browserify while walking through building an app in React.
Don't get confused, pick one and work with it, you will learn more in the process.
React is just the UI layer. Facebook uses an architecture called 'Flux', it complements React's composable view components by utilizing a unidirectional data flow. You can follow roughly these steps to learn how to use React and Flux together.
At this point you would need a way to route things. React-router is the best option I know of.
Give this repo a read at the end. This puts together everything so far mentioned into one tiny working project, this will clarify a lot of your doubts.
As you explore, you will see tons of options again! Yes, this time about which Flux implementation to use - Reflux, Alt, Fluxxor, Flummox, Redux, Fluxible etc. But at this point, you will be good enough to decide which one suits your requirement.
At Hashnode, we are using Alt to build isomorphic web apps. Here's a tutorial by @sandeep on how to build isomorphic javascript web apps with Alt. Redux is also a pretty great option and is getting hotter every day, here's a nice article, a hands-on tutorial and a course by Dan Abramov (creator of Redux) explaining Redux.
I have two collections Learn React and Learn Flux, which I keep updating whenever I find something interesting in React and Flux world.
Happy Learning!