This download looks like a lua file. You need to place it in your lua folder inside the Garry's Mod folder.
You should end up with a directory structure similar to below:
Don't know where the Garry's Mod folder is or how to extract zip files? See more useful installation tips.
XXFalconFuckerXX 6609, borisdremdjiev12, -AS-Veilleur, dboese, vebios123, damian123, Deus0331, gabimagloviti, domlovezte, babaarda2005, VCayres, EMDQ, nemanja.matic.stanivuk, remarpc, Fort, Fort, Fort, Fort, gerod.ford, Dr.Doctor