Placing a new bet
Click the corresponding price cell. An order ticket will pop up enabling you to check the order before it is sent (unless you have turned the One-Click feature on).
Modify an existing bet
Click anywhere on the bet in the 'Working Bets' list. An order ticket pops up for the corresponding order, enabling you to change its stake, odds or persistence type.
Cancel an existing bet
Click the 'X' button on the corresponding bet, in the 'Working Bets' list. There is no message asking you to confirm your decision, the bet is simply cancelled immediately.