Amplifiers boost the power of a PWM signal from a controller. This lets the controller manage a much bigger lighting load than it could on its own.
The PWM signal could be 1 channel (white light), 2 channel (CCT adjustable), 3 channel (RGB) or 4 channel (RGBW).
To boost the output signal, amplifiers require power from a low voltage driver.
A receiver takes a signal from a controller. The type of signal depends on the controller used.
Powered by a low voltage driver, the receiver adjusts the lights connected to it as instructed by the controller.