Refer to figure.
In a helicopter:

Throttle

• The throttle controls the engine power, like in a car.
• In some helicopters, the pilot has to adjust the throttle manually using a twist grip on the collective lever, which controls the helicopter's lift.

Governor

• The governor is an automatic system that adjusts the throttle for you.
• It keeps the rotor blades spinning at the right speed by increasing or decreasing engine power as needed.
• This helps maintain a stable flight and reduces the pilot's workload

Summary: The throttle controls engine power, and the governor automatically manages it to keep the rotor RPM constant.