For a horse with those odds, you would have to bet $5 to win $1 -- plus get back the amount you wagered. But there's a saying around the track: If you've got the $5, why do you need the $1? That's why some bettors snub the favorite and take a horse with higher odds to improve their payout. (Like the people who bet on Birdstone in the 2004 Belmont Stakes. With 36-1 odds, the longshot beat Smarty Jones, the horse favored to win the Triple Crown. In that race, a $10 wager on Birdstone returned $370.)
Another way of looking at it is to say that 5 out of 6 times, a bet on Big Brown to win would return something, whereas only 1 time out of 6 would the other bet return money. That's the whole idea of "odds."