Really dumb rookie question

Hey everyone first please excuse this question.

I am new to the Max 2 it just came Monday. I have Kindle books, and also Google play - those apps work fine but I really want to use Neoreader. The dumb question what is the best store to buy epubs that will work with Neoreader - or do I need to try and convert everything to epub.

Is there a store I can just download - I am assuming now and I have to use conversion software?

Again total rookie question, but I am little stumped on this one.

Thanks in advance,