A home theater A/V Receiver and Amplifier assembly actually combines several different components. Some of which have a DVD or other media player built in. You can generally assemble a superior home theatre system by buying the components separately, but most people buy one unit that does all tasks because it’s more cost effective.
The Receiver’s components are:
The path of the audio and video is pretty straightforward. The source component (DVD player, DVR, etc.) feeds a signal to the receiver unit. You choose which input component you want to feed to your output unit, and the preamplifier selects this signal and amplifies its line level a little bit.