This is a setter function that allows you to set the throttle variable. Once you set throttle, you have to use move() to actually execute the movement. The throttle variable will remain what you last set it until the end of the flight sequence, so you will have to set it back to 0 if you don't want the drone to throttle again.
power: An int from -100 to 100 that sets the throttle variable. The number represents the direction and power of the output for that flight motion variable. Negative throttle is down, positive throttle is up.