What is RMS and how do i know how loud i can play Car subs without Blowing them Exzmple Like 12's?

RMS is your continuous power handling, peak represents what circuitry can handle for approximately 1/32nd of a second. Your best bet is to purchase an amp that is equivelant to the subs ratings, ideally the lower the amplifiers THD (Total Harmonic Distortion) the less possibility you have of overdriving your subs. Beware overpower, underpower or driving distortion (bass boost features) as these will all result in either voice coil or cone destruction.