The official documentation offers a pretty good starting point : facebook.github.io/react/docs/getting-started.html

I would suggest the following learning path :

1. Start with the documentation and follow the steps outlined there. Take a look at the Guides and Reference section present in the sidebar. Once you get the basics you should read those.
2. Create a very simple app using React - Not necessarily a note taking or todo app.
3. Learn about Flux architecture here : facebook.github.io/flux/docs/overview.html. These libraries help you implement Flux easily.
   1. Alt : github.com/goatslacker/alt
   2. Reflux : github.com/spoike/refluxjs
   3. Fluxxor : fluxxor.com
4. Now implement your sample app using Flux.
5. Create a slightly more complex app using React and Flux.
6. Once you are comfortable with this, learn to create isomorphic apps using React. The following resources will help you out :
   1. smashingmagazine.com/2015/04/21/react-to-the-futu…
   2. blog.risingstack.com/from-angularjs-to-react-the-…
   3. egghead.io/lessons/react-development-environment-…
   4. blog.engineyard.com/2015/client-side-javascript-p…
   5. christianalfoni.github.io/javascript/2014/08/15/r…

P.S. If you want to go with Isomorphic apps do check out Alt. I have had nice results with this.

I'm new with React as well and the two best sources I could find for starting out are 'React Fundamentals' on pluralsight and 'React' by Ryan Florence on Frontend Masters. Unfortunately, neither are free to access.I also recommend following @ryanflorence and @mjackson because they are heavily involved in the React community and they have some good insight.