Most microcontroller outputs can only drive tiny loads. They are good to drive a few LEDs but for anything more, they need a little help. For servos and small motors, we can switch a transistor, which can handle the larger current. When we want to controll something more substantial than a that with our Microcontroller or Arduino, a Relay can be a cost effective solution.
These relay boards can handle 10A of up to 30V DC or 250V AC
They only require 5V VCC
Logic signals are 5V compatible.