Thanks! I think the best way to get started right now is to grab the official Facebook create-react-app package, pick something you think would be fun to build, and just start trying to build it and googling/asking questions along the way. The first project might suck, but that's okay. You'll pick it up fast, and the next will be better.

React + MobX is my favorite way to build frontend apps now, and MobX does help a lot in terms of development speed, maintainability, and performance, in my experience. If you're brand new to frontend development, I wouldn't worry too much about it, though - it can be best to start with the basics initially.