Usually a motor will give a recommended amp draw, say 15 amps. Any more than that and the motor could be hurting, such as overheating. Pick a prop that will get to that many amps without going over. Pick an ESC that will be at a higher amp rating than what the motor is. As you see, if the ESC were rated at 10 amps, it would overheat if asked to put amps through what the motor is asking for. 3s2p means 3 cells in (S)eries and two batteries in (p)arallel. The three cells would be 11.1 volts. The 2 in parallel would give you twice the amp draw of a single batt. or twice the flight duration. If this isn't clear holler at me. A good tool to get is a wattmeter in order to tell you how many amps the motor is drawing.