You're able to pick the sign up bonus you want to start wagering alongside bet365 with when you type in PINEWS as your bet365 bonus code when prompted during the registration process.
When you place a bet using a Bonus Bet the winnings are calculated differently to a cash bet. A bet placed with a Bonus Bet will pay out the winnings minus the Bonus Bet stake. For example, if you placed a $20 Bonus Bet at odds of $10 your winnings would be $180.