If you bet on the guy that's expected to win with 1:1 odds, and the guy wins you multiply your stake by 1.0. If you bet on the guy that's expected to loose by a 2:1 margin and and the underdog wins, you multiply your wager by 2.0.
Ex. Liddell vs. Ortiz is currently running at 3:1 in favor of Liddell. If you bet say 1000 points on Ortiz and he wins (which he will not) you triple your money. But because Liddell is expected to win it would be a push if you bet on him.