Read the odds out loud by pronouncing the colon as "to." For example, if the odds are 2:3, pronounce this "two to three."
Add the two numbers together to understand what the ratio means. Think of the ratio as describing a beanbag toss game, and the sum of the two numbers as being the total number of times a player throws the beanbag. In 2:3, he would throw it five times.
Check whether the number before the colon or after the colon is lower, remembering that the number to the left is the likelihood that the event will happen. If the lower number is to the left of the colon, the odds do not favor the event. For example, if the odds of Michelle winning a beanbag toss game are 2:3, she will win two throws out of five and lose three throws, making her slightly more likely to lose. If the lower number is to the right of the colon, the odds do favor the event. If Michelle's odds are 3:2, she will win three throws and lose two, making her slightly more likely to win.
Read odds against something by remembering that the positions of the numbers are reversed. If the odds of Michelle winning her game are 3:2 against, this means she will lose three tosses and win two. Odds against something represent the likelihood that it will not happen, rather than the likelihood that it will happen.