Understanding RF power amplifiers

What is an amplifier?
A device that uses a small amount of energy to control a larger amount. The relationship of the input to the output, expressed as a function of the input frequency, is called the transfer function of the amplifier, and the magnitude of the transfer function is called the gain.

What is RF? What is an RF tuner?
Radio frequency (RF) is the range of electromagnetic frequencies above the audio range and below infrared light (from 10kHz to 300GHz).
RF tuner
An RF tuner is a circuit module or standalone equipment that detects radio-frequency (RF) signals usually of low amplitude and amplifies and converts them to a form suitable for further processing.