Quake was the first true 3D game that I have edited for, and so some of these levels are more primitive than my levels for other games. Towards the end of my Quake editing, with the Water Treatment Plant and base of the 12 Monkeys, my maps became more advanced.
To run Quake levels, simply place the map in your quake\id1\maps directory. Once in the game, use either the "map" or "changelevel" command in the console to switch to the map. For example, if you downloaded vr, you would type "map vr".