The motor converts the electrical energy stored in the battery to kinetic energy. When choosing a motor there are a couple of things to pay attention to.
KV: The KV value indicates rotations per volt per minute. That doesn't necessarily mean more = better
Brushless / Brushed: States whether the motor uses carbon brushes for control or an ESC. Brushed motors have got a higher maintenance requirement, because the brushes need to be replaced, but are cheaper. If you use multiple motors you'll need only one controller if you go with brushed. Brushless motors on the other hand are more efficient and offer more power.
Sensor / Sensorless: This is especially relevant for the choice of ESC. A motor with sensor, when combined with an ESC that can read that sensor, has got more torque in the lower rpm region and starts more cleanly, because the ESC knows where the rotor in the motor is at all times and can power the correct phase of the motor. Sensorless motors start up jerky and tend to stutter when they start to roll. this may throw you off balance