Relay Module 10A 4 Channel
You may use a relay in controlling high-voltage components that your MCU could not, may it be AC or DC.
A relay is a mechanical switch. What it does is to allow a current to flow or not, through the signal it receives. It has 3 terminals: Common, Normally Open, and Normally Closed. It also has 1 coil that does the cutting or allowing the current to flow. As for the terminals, the Common Terminal and the Normally Close terminals have the continuity without energizing the coil. When energized, the Common Terminal and the Normally Open Terminal will have the continuity, and cutting the connection to the Normally Close Terminal.
The Arduino's 5V digital pin can control this relay. The max control capacity is 10A @ 250VAC or 10A @ 30VDC.