Moneylines are the most common type of bet in any sport. This is where you back a team to win a game.
Point Spreads are also a common type of wager on MLB games. This is a wager on the margin of victory, so you will win more or less, depending on how much a team wins or loses by.
When it comes to a more baseball-specific type of bet, 5-inning lines are a very popular form of MLB bet.