Hi Elizabeth, great question! Relays are commonly found in many electronic applications. They are useful because they allow a small amount of power to switch a larger amount of power. Electromechanical relays perform this function by using a coil and mechanical contacts.
To activate a relay, current is applied to the coil – energizing it, creating a magnetic field which pulls in the contacts and either closes the circuit for NO (normally open) contacts or opens the circuit for NC (normally closed) contacts.