Popes are elected by Cardinals of the Roman Catholic Church. Once they are elected they hold the job for life. Until the nineteenth century, the Pope had a lot of political power. This is no longer the case.
Pope comes from the Greek word pappas, "father". Catholics believe that when making official stements about belief (ex cathedra), the Pope is infallible - that is, God will not allow his followers to be misled by allowing their leader to make a wrong statement. Very few of the Pope's statements have been ex cathedra in recent times.