If you win your first bet, then your entire return (stake plus profit) will be staked on bet two. If you win bet two, then your entire stake plus profits will again be staked when you placed bet three. This is why it's known as a rolling bet.
Out of each wager placed through OTB, approximately 77 percent goes into the parimutuel pools for distribution to winning bettors. The remaining amount, known as the "takeout", is retained by the OTB operator. In addition, a surcharge of 5 or 6 percent is deducted from most payouts to winning OTB bettors.