For a Quinella bet you must pick the winner and runner-up of your race; however, other than in a Exacta/Perfecta bet, the order in which your horses cross the line does not matter. As long as the two horses on your betting slip are ranking first and second - either which way - you have won. This kind of bet is a great way for a new bettor to built up skill and confidence before moving on to the more restricted Exacta/Perfecta bet.
For example, you have bet on EternalSunshine and Crank in a Quinella. This means you will win if these are the first two horses over the line. Again this is one bet including two horses, which are not bet on individually and will only win you a pay-off as a set. If EternalSunshine comes first or second for instance, but Crank finishes third you win nothing. Likewise if Crank takes first or second place while EternalSunshine only manages fourth, you leave empty handed. However, although both horses are needed for a win, your chances are still higher with a Quinella than with an Exacta/Perfecta bet, since the order of the horses does not influence the pay-off.
As with the Exacta/Perfecta bet, the odds of a Quinella bet depend on the number of horses starting in race. Considering that a larger number of horses makes it less likely to pick an accurate Quinella, a race with seventeen horses will offer a larger pay-off for a Quinella bet than a race of seven horses. Also, as the exact order of the first two horses is not important, the odds for a Quinella bet will always be lower than those for an Exacta/Perfecta.