A cam is a very simple mechanical device that you find in many different applications, from sewing machines to car engines to timer motors. All it is is an oval-shaped disc attached to a shaft. If the shaft rotates so that the long part of the oval is facing an actuator, the actuator will get pushed down. In the case of a timer motor in an appliance, this actuator would be a switch contact.
This demonstrates their action pretty well:
It basically opens and closes switches.
You don’t need to know all of these details for now- you won’t be quizzed on timing charts. We just want you to get introduced to them.