TL;DR:
If your game then or , alternatively here's .
You probably just bought Gmod and joined a server only to be greeted by , am I right?
Don't worry, there's actually nothing wrong. I know it looks bad but that's pretty normal, (if you plan on playing Gmod, or any Source Engine game for that matter, you'll run into this a lot) and easy to fix. The most common reason why you're seeing this is that you don't own/have Counter-Strike: Source installed and mounted to Garry's Mod.
If you don't already own then I'd recommend buying it while it's on sale for the holidays, however, if you don't want to buy and install a game you'll probably never play then you can follow . Alternatively, if you prefer here's one that shows step by step what to do.
A user on our Discord made that will extract the CSS content you need using SteamCMD for you. I highly recommend using it if you're having trouble doing it manually.
If, however, you already own CSS then:
