The quick answer: My Wagers are unrevealed payouts.
The long answer: When you wager with b spot, you're placing bets on live horse races. Once your wager is confirmed, the funds are wagered. My Wagers represent the money you placed on the race.
After the race results are finalized, you use My Wagers to collect your payouts while playing games. All your payouts then go directly into your Cash Account.
Remember, you cannot make a withdrawal from My Wagers. They have no monetary value.