Bakugan Traps may only be played after the gate card has been opened. Your bakugan trap attribute must match the attribute of the bakugan your battling with. When you shoot your bakugan trap in, your gain a boost equal to the amount of G's your bakugan trap has.
Bakugan trap abilities still count as your card chances. You don't get any extra card chances unless your bakugan trap has a special effect (Hexados for example).
(M_D may edit this)