For each competitor you'll see three sets of data underneath their name - "To Win", "Payoff" and "Pool". Each of these numbers provide you insight into how other bettors are wagering on each competitor. All of this information is there to simply help improve your chances of making a winning wager.
To Win - The percentage indicates, of all the people who are wagering on the runners, the % that think this runner is going to win. As more bettors place wagers, the odds change. So who was the "favorite" to win 15 minutes before the race may not be the favorite by the time the race goes off.
Payoff - This is really the POTENTIAL payoff on a wager to WIN, based on the current money in the pool and the number of people who've wagered on that particular runner. Remember, this is pari-mutuel wagering (meaning the winnings are based on how much money is bet by all the players), so the payoffs are calculated based on the money in the pool divided by all the people who placed a wager on the winning runner. So the payoff gives you an idea of the POTENTIAL payoff you will get by wagering on that runner.
Pool - This is the amount of money that has been wagered to win on the particular competitor SO FAR. So if you add up all the money in the pool for each runner, you get the total amount bet TO WIN on this particular race
"Favored for 1st, 2nd, 3rd" - This indicates the top three picks by other players. Meaning of all the people wagering on this race, the majority of people think that these competitors are the most likely to win.
Hint: It's all pretty straightforward, all these numbers just really relate to how many people have placed wagers on a particular runner to win. If you're confused or want to just "dip your feet in the water" before trying to guess a winner, place a "show" bet on the competitor with the star next to it. This means you're betting that this competitor will come in first, second or third in the race. Your payout will be less, but your chances of winning are greatly increased!