The winner is the one who is either still standing ( as in, it's 3 mins per round, times 12, title on line only or a nontitle fight is 10 rounds, if you knock the other guy out within the 3 mins you win it's called a KO, or if you hurt the guy and he trys to get up but he's not on his feet before the count of ten seconds you still win.
Or if you cut the other guy ( it's normally above the eyes ) and the ringside doc says it's too bad to continue you win by T.K.O.
Or you go 12 rounds it go's to the judges score cards ( each round is scored be 3 judges 10 points each round ) if you win most of the rounds you get the win.