Superheterodyne LO question
 

I am trying to get a handle on superhet design and keep getting stuck
on the local oscillator portion. I've been wading through the ARRL
handbook and some other resources, but I can follow exactly how the LO
signal is created. Is the signal generated entirely in the radio, or
is the signal generated from the RF picked up from the antenna, or am
I so off base that neither explaination is right?
As an example, if I wanted to make a single frequency receiver could I
just use an external fixed oscillator for the LO signal?

TIA

Liam