If you lose you pay 10% extra. Bookies will try to have even action on both sides and not have to worry about the outcome because they'll make 10% of the total bets. Often times this doesn't happen and it will be one-sided. They either take the risk or lay some of it off to another book.

The two most common bets are point spreads and over/under for football and basketball. For example, say the Bears are playing the Packers and are -7 (I wish), this means that the Bears are favored to win by 7 points. If they win by anything less than 7, the Packers would win in betting terms. Over/Under is betting the total score. So if the over/under is 51 that means that the predicted score is 51 so you either bet over 51 or under 51.

For sports like baseball and hockey the scores are too low for spreads. Say the Hawks are playing the Sabres, if you bet the Hawks you will bet 230 to win 100 (hypothetical).

Hope that helps, I'm sure there are others on here who can go into greater detail.