Washing machines that load from the top have a circular spindle in the center of the tub called the agitator. The purpose of the agitator is to mix up the water and clothes once the soap and water have been added to help remove the dirt on the clothes. During the agitation cycle, it moves back and forth in quick motions to mix up the water. During the spin cycle, the agitator spins at high speed to help remove most of the water from the clothes.
Start a load of laundry but do not close the door once the wash cycle has started.
Locate the open door sensor for the lid of the laundry machine. It is often a small button at the back of the lid that is depressed when the door is closed and released when the door is open.
Press in on the sensor once the water has stopped adding to the tub. This should activate the agitation cycle. Use a screwdriver or pen to help push in on the button if necessary. The agitator should start to oscillate back and forth, mixing up the clothes in the water. If the agitator does not move, double check that the sensor is depressed. If it still does not move with the sensor depressed, the agitator is broken and should be repaired.