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.
YurIsLuv, YurIsLuv, Lucky, [Rainbow] Goofigaboo Gooberikku, Busty The Nut, Kms, scottlluch, 심심한 퍼니, DequanJohn, NOT Cake, Vermillion, chewy, A p p l e, JustEd, Voidacity, Natium, SharkBait, Leon Kay, Мастер Гервант, Keshwoof, Perfect バービー, Tim