You must download the "Source Engine Base" content packs.
By the time you spend 4 hours hunting for a tool to download Workshop files, converting .gma files, hunting for CSS textures, and troubleshooting LUA errors, you could have: how to mod cracked gmod
: Copy the Steam Workshop URL of the mod you want and paste it into a tool like steamworkshopdownloader.io to generate a manual download link. You must download the "Source Engine Base" content packs
: Boot up GMod. The mods should appear in the Addons section of the main menu. Troubleshooting Tips How To Get Mods In Garry's Mod (Gmod) - Step By Step converting .gma files
Without CSS textures, you will see signs and pink/black checkerboards everywhere.