hi

i'm pretty sure i will be using this forum a lot however i am not sure where to start. specifically at the moment i am going to do a lot of travelling from June 18 onward longhaul mainly. I have a few questions and a quick search didn't get me the answers one hundred percent.

how many frequent flyer programs are there?
what are the best ones for travelling long haul?
can i claim on flights i have already flew on recently?
Thanks

Paul