what exactly are demos

[yoda16]

Are the demo files just what you see when you start quake and it plays by itself.  I downloaded fragtown and thought it would be a new single player mode but I see the new demos playing untill i start a game then I get the regular game.  how and where do i get new single player games.  I can start the fragtown levels in multiplayer and put in omicron bots but i wanted to see if i could get whole single player games.

[Moose or Chuck]

Well, an entirelly new single player game would be called an Episode. There are also mods that can give you a new single player game. I doubt fragtown is a single player map as well as a multiplayer map, but it would say either way in the readme that would have come with it.