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.
OverlordTrumpDump, [DFS] NaDE, aeslami111, Manchester 25, sshahrabadi92, artak.sargsyan95, artak.sargsyan95, -[Izakian Private]- Michael M, skuyzy, FluBuddy, Le Muffin Man, С14.MPF.OfC-211.Lovr0, Tornado-Torben, Wolfgang615λ, pepa.kopinec, j.eric.lowe