When do i start raiding? i don't know where to start

I have a level 80 character now and have been grinding heroics for a week now. My WotLK Items are much better than before but how well does it need to be? Every time I see people asking for people raids but I have yet to say "me plz" because I just don't know if my gear is even good enough.

So is there a "must have" kind of list that one can follow to know if one is ready to go into raids? I would hate to be the underaged guy that just doesn't contribute to the group. And I would hate it even more if someone I wrote, would turn me down bec of gear issues.

I'm really confused as to how people always know when "they are ready to raid".

I also don't have a guild bec I'm too afraid to find one so that's probably an issue.