Basic installing information Thread

Most Steam related games/mods already have instructions bundled together with them. I reckon it is you first time working with Steam?.

I haven't really played Gmod for a while and especially not the recent commercial versions of this mod, but here's a generic guideline that works for most games/mods made on Steam:

1. Shutdown Steam before installing Gmod.
2.  Begin the installation/downloading process  and let it fully finish.
3. After it is done, open up Steam again.

You should see Gmod up and running in the "Libary" tab, double clicking on it should execute it. The rest is simple.

You should really try to visit the official site or the Gmod's Wikia page for more support or information on how to correctly play the game.