New to uber lots of questions....

Hi! So I popped my uber cherry last night and was pleased with my $81 take home (not including gas ...I know) but I have lots of questions...so please bare with me! First, while reading the forum what does PAX and FIFO stand for? Also if a rider cancels after I have arrived and passed the 5 minutes they are charged $5 ....who gets that $5? I read that some of you text the rider before the pick up but how do you do that? I only see an option that says they are notifying the rider and twice I had the rider call me but that's the only way I would have their number?? How do some of you know where the rider is going before you get to them? I see some of you say you get a ping and accept and then cancel when you see where they are headed. And one last question....for now... A friend who also drives for uber got a ping for a rider while in route for another rider....she canceled it and then it continued on to original destination only to have it canceled. Why would you get a ping for a rider during a another trip? Thanks for your patience in advance❤