Verify that you do have your ESC plugged into the throttle channel for your radio/reciever
You probably need to calibrate your throttle with the ESC/motor. This differs with each type/brand of ESC so you may want to look it up for yours if the following doesn't work.
With the battery unplugged but the radio turned on... and the prop on the motor removed ( for safety just in case ). ( desciption is for a plane/heli, so perhaps take the wheels off for a car/truck )
Raise your throttle to full throttle on the radio.
Plug your battery in on the airplane
Lower your throttle to the lowest setting on the radio.
In most cases, that will calibrate it and allow the ESC to arm ( or activate for another word for it, usually you'll hear some tones from the motor if it does ). If not, the trim for the throttle on the radio may need lowered... try clicking it one click at a time and repeat it until the ESC finally arms during the calibration steps I mentioned.
As I also mentioned, not all ESC's use those exact steps. If yours isn't arming... read the manual for your ESC to find out the steps. Please note that the ESC must sense a zero throttle setting also for it to arm so you may need to tweak the trim until that happens. I'd also suggest counting the number of times you click the trim down in case you need to get back to where you started at.
