Gearboxes can provide 3 basic functions:

Change torque and speed	Change axis of motion	Convert rotary to straight line motion

Major application of gears is to change the motor high speed / low torque to low speed / high torque usually required by applications.

High Speed / Low Torque

Low Speed / High Torque

Torque Tgear = Tmot • ratio • η (η …gear efficiency)

Speed ngear = nmot / ratio