Subject: How does a rocket propulsion system work in a vacuum (ie. space)?

How does a rocket propulsion system work in a vacuum (ie. space)?
My question might seem a bit arbitrary, but it has entertained my
fellow scientifically uninformed companions and I for many an hour over
an evening beer.  I am aware of what Newton had to say about this (for
every action...), which I can understand in a "world-around-me"
context, but if there is nothing for the rocket to exert a force upon,
how can an equal but opposite force be extracted?

I would greatly appreciate any informed persons sharing their
enlightened views on this with me, or anybody else who has anything to
say.

Thank you.

Clive

Re:How does a rocket propulsion system work in a vacuum (ie. space)?