Iamnot,
Hope you do not mind if I abbreviate your pseudonym...
After the previous informative reply, perhaps a little more.
Basically, a radio consists of a receiving part and an amplifier part. The receiving section selects a specific station out of many hundreds, and processes the audio signal(s) off the radio wave. This delivers a small audio signal (order of millivolt). The amplifier part then amplifies this and finally feeds a large signal to a power stage to drive a loudspeaker. Thus all radios, from your portable to the most involved av system, consists of a radio part and an amplifier part, which may have several separate amplifiers for the respective channels.
On the classic hi-fi scene one normally had separates connected by cables, whereas on the av scene these mostly come combined into one fairly extensive unit, but internally still consisting of the separate units, integrated in whatever way you desire by switching options, etc.
That basically: hope it starts things. By the way, there are no stupid questions, just stupid answers. As the saying goes: He who asks is a fool for five minutes; he who does not ask is a fool for the rest of his life.