The Gmod community is one of the worst I have encountered when it comes to giving clear and correct instructions for installing their mods.
If you're lucky you'll get a vague description telling you to stick the file in some location on your HD. The problem with Gmod is that a lot of the cooler mods are highly dependant on other mods to make them work correctly and the community is horrible for providing you details about what mods are required and chances of actually getting a link to the required mod is a pipe dream.
The other aspect of the community is the trial and testing that's done on some of the mods. Some of the mods out there will very quickly reduce your computer to an unresponsive pile of electronic bits and plastic mainly due to
a). Require mods that the author hasn't bothered to tell you about
b). Poor or incomplete mods
Gmod is a step learning curve, things like Wire mod require a basic understanding of logic gates and whilst I was learning to use it I was unable to find anything that came even close to a readiable help guide. You'll get more out of Gmod by learning how to do things in it yourself, it's also the hardest way of going about it and you will suffer more than the occasional mess up but it's generally worth it oh and PS check out my Paladin auto turret over at the Gmod files site.