Power supply unit is an Electronic circuit which is used to convert 220VAC supply into 5V/12V DC supply.
Micrcontroller is a small computer and reprogrammable device which is used to control embedded system devices.
Relay is an electro-mechanical device which is used to control High power AC devices from Low-Power control signals.
Motor Driver is used to drive DC motors in either directions by help of microcontroller input signals.