Delegating on Yoroi

I’ve held ADA for over 3 years now but haven’t really been paying attention to it too often. It came to my attention that I could delegate the coin to earn more back. I have a question on the process to do it. I transferred my ADA to Yoroi already but don’t know who to delegate to. Is there a way of telling who’s good and who’s bad? Also there’s a cost (I.e 2.80% {1.90% + 340}). What is that mean?