There are generally two types of betting straight up and money line bet or point spread bet.
Straight up bet and money line bet is commonly used the spots like baseball, hockey, soccer and individual events like boxing. The payout for such events is quoted as a single bet unit. That is a team or person having a chance to win in the ration of 2:1 will be listed at a price of 1.50 where as the team that has less probability of winning will be listed with a price of 3.00. This type of betting is commonly used in Europe and Asia in sports where the point spread is not practical.
The money line bet America is different.
Here the bookmaker quotes the amount based the $100 to win for the favorite. The amount won will be based the amount that is betted on. If the team which is the favorite wins the better will get $100 and if the underdog wins the better will get $300. For example consider a football match between Brazil and Portugal. Brazil is taken as the favorites at an amount of -200 and Portugal the underdogs at +180. The person who bets for Brazil will have to risk $200 to get $100 if he wins. But a person betting for Portugal will get $180 for every $100 he pays. The 20 cents that remains from the share of the loser is taken as the commission by the bookmakers.
The money line bet requires only the team or the person that the bettor selects to be won.
Once his side wins he gets his share else loose it. There are situations in sports like football, baseball and cricket in which some teams are considered to be favorites by a huge margin, if the opponent is weak.
In such cases the quote may be -400 or higher. So the person betting on the favorite team has to put a huge amount of money at stake. A person supporting the weak team will get a huge sum in return if it somehow wins. This is often the major factor that leads to match fixing.