Sexy time: Top match Bottom?

I always wonder about the role in gay sex, is it must be top with bottom, which one is "giver" and another is "receiver"?  I know there is versatile sex role, but can two totally bottom gays be together and have good satisfacion in sexy time. I mean sometimes you as a bottom cannot control yourself to fall in love with someone who is bottom, and you can simply reject this feeling because he is no a top.

For lesbian is the same concept which both of partners are "receiver", yet they seem work well with each other. Not sure whether bottoms must want people to f*ck them in sexy time, only can get the satisfaction. For myself..still discovering my role preference, but mostly I think I am a bottom. Well, I still have ZERO relationship experience so do even say about sex experience. Therefore, I totally naive and ignorant about it.  

My gaydar is kind of not functioning, maybe because I suppressed my feelings too much so it doen't develop well. I only can identify those with some obvious signs like feminity, but not all "sissy" guys are gays, so I still kind of stuck. Bad habit for me is when I see a hot guy, I will keep trying to look at him. Sometimes is kind of obvious, but kind of manage to control facial expression so it doesn't look like gay-ish peeking and staring. Normally, I think those who are feminine are bottoms, so not sure how to differentiate top with straight guy. However, I found that by listening to their voices is sort of a way to identify, not sure how it works but depends on sixth sense?

Anyways, I still new in this area so forgive me if I asked some stupid questions. =)