Can someone tell me how to download a background on garry's mod?

I can’t figure it out!!! What folder do I save it to?

Well usually most are in addon folder download types. But I believe somewhere in materials or something. I just extract it, open it up, high light all folders I see and not text document files of course, then go into my Garry’s Mod 10 directory and high light the matching folders, then paste, and it does the rest by itself and put sitself where the files from the download tell it to. If you already did this you apparently didn’t high light all the folders, or the download is just a bust so try another!