The pope began as the archbishop of rome, who was, supposedly, first peter. Among other notable events in Peter's life, he denied following Christ three times, and Jesus told him "You are Peter, and on you i found my church." Peter in Greek--i think--is Rock, and so it makes sense. On this relatively thin line of scripture, the Pope became the most important bishop. He is elected by the college of cardinals. The current pope was Karol Wotijwa (sp) from Poland before he was John Paul II. The history of popes is rather screwy. It wasn't until the thirteenth century (if memory serves) that the pope became infallible; that is, when he makes a statement from the chair of saint peter about something religious (the exact specifications elude me) he cannot be wrong. Popes have only made two infallible statements to date: that Mary was immaculately conceived (not Jesus) and that Mary was assumed into heaven. There's no scriputral basis for either. A famous pope (Caesare Borgia) had a kid with his daughter while pope. Another, we'll call him Innocent or Urban, exumed the body of his predecessor to put him on trial. He cut off the past pope's hand and buried him again. At one point there were three popes at the same time.
There isn't a convenient way for the pope to step down. Right now (post Vatican-II) he's more of a figurehead than anything, though his power is still significant. This current pope said he didn't want priests to marry, nor did he want women to become priests, and so neither is the case. He could still say something infallible, but to put it mildly, there's strong incentive that he not do so. He's made a number of apologies, among which were being sorry that, erm, I think Paul XXIII (or so) wasn't quick to condemn the holocaust, and he was sorry for the crusades, etc. The pope has been sorry for a whole lot, but he hasn't done much to change it
If you have any specific questions, I'll recommend some books if i can't answer them myself.