jenstar is quite correct.
The Tragical History of Doctor Faustus is a play by Christopher Marlowe, based on the Faust story (Faustus is Latin for Faust). In the fanciful tale of Dr. Faustus, a man makes a deal with the devil: in exchange for his body and soul, the man is to receive supernatural power and pleasures for 24 years. The devil agrees to the trade, and Dr. Faustus enjoys the pleasures of sin for a season, but his doom is sealed. At the end of 24 years, Faustus attempts to thwart the devil�s plans, but he meets a frightful demise, nonetheless. So that�s the why (supernatural powers and lots of sin, can�t be all that bad eh!).
The second bit. There is no mention of anyone selling their soul to the devil in the Bible nor that it is possible to do so. But if someone wishes to submit to the temptations of sin, then they are effectively submitting themselves at the will of the devil (Satan has dominion over those who live without Christ in the world etc). Another way is to join the Church of Satan but the annual subscriptions to that would probably cost you more!