I would say stick to basics. First, read up about all the different kinds of components which RN gives you out of the box.
You can also check out Nativebase which gives you a bunch of customised components in its kit.
How to start? I would suggest you to use Expo along with Genymotion. Set up your work environment and use Expo's boilerplate for a new app. Expo's documentation is crazy good, so make sure you read it.
I hope this answered your question. If not, do reply. :)
Cheers and happy building! 😄