12" x 12" is the SIZE. The power could be anything. If you don't have the specs, measure the voltage with a multimeter on a sunny day. You said it was good for an amp, right? Use ohm's law to put a resistor on it to load it down to an amp, and measure the voltage again. The first reading is the float voltage at full sun (or close to it) and the second is the loaded voltage. The motor will need to turn at the loaded voltage.
Not sure what diagram you are talking about - got a link? What I described is a pretty standard way of doing it on the cheap, though. A better system uses a microcontroller.
Got to warn you, what these guys are talking about with the motor energy is a real issue. The problem arises that when you subtract the total energy to turn the thing from the reduction in total energy from not being perpendicular all the time (motor works against wind forces, and some days are overcast), consider the loss of reliability, added complexity and so forth, it doesn't often pay to tilt the panel. That's why most solar arrays just lay flat.