The ESC must match the motor and prop for a plane of given weight. The combination will draw current from the battery pack and the rate at which the current draw happens will determine what ESC you need. Also, if it's a brushed or brushless motor makes a difference.

Find out the overall weight of the plane and decide how you wish to fly the thing. Look at the top of the Beginners Forum for a "sticky post" titles "Prop Chart and Basic Electric Setup". Within that sticky thread is a post that has "power to weight" and pick a flying style.

Note that this will refer to the maximum power that the ESC/MOTOR/PROP will draw during flight. Power = watts. Watts = Current x Voltage. The voltage is fixed at the number of cells in your LiPo pack and the arrangement (series, parallel, or series parallel). Most beginner packs are series and at 11.1 volts (nominal) per 3 cell pack. So, that's a "constant". The variable is the current draw. If, for instance, your plane will draw 20 amps max then the wattage here is 11.1 X 20= 222 watts.

The power required for various types of flying styles will give you some indication of what you will need for your plane.

You must take the entire weight factor into account, meaning the fuselage, servos, receiver, battery pack, ESC, motor, prop, everything. Get the weight and factor this in to determine what the wattage will be and figure out the current draw and buy the ESC accordingly.

Since you probably don't know what you need, you have to do a little research and do some calculations based on what you find for various combinations. A mail-order web site like Tower Hobbies gives a detail for each component such as dimensions, weight, and so on that you can use in your calculations. It comes down to a pick and choose method for trial and error until you get the combination that will work.

Yes, it can be a PITA but unless you already know some of the info, you have to do the research.

Good luck.

CGr.