spy_night_vison_googles_hexed.

This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • Spy night vison googles Hexed <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• Spy night vison googles Hexed/
  • materials/
    • models/
      • Nightv/
        • items/
          • spy/
            • spy_hat.vmt
            • spy_hat.vtf
  • models/
    • Nightv/
      • items/
        • spy/
          • Nightvi.dx80.vtx
          • Nightvi.dx90.vtx
          • Nightvi.mdl
          • Nightvi.sw.vtx
          • Nightvi.vvd
  • settings/
    • spawnlist/
      • Spy night vision googles hexed.txt

Koopashell TMK #Meem, The Wolf Street, Fabio, [EVO]_Manolo_[FR], Cute_Bonnie1987, ☣ Vexer Wor ☣, ☣ Vexer Wor ☣, Warpath-the-drone swe, LazerSpy, LazerSpy, PeculiarPsychopath, [S.e.S]^Mr.Bondy