1. Download SteamCMD and extract it to its own folder (e.g. a new folder on the desktop).
2. Open the SteamCMD folder and ensure that "File name extensions" is enabled under the "view" tab in Explorer.

3. Create a new text file by right-clicking inside the folder, and rename it to cs_textures.bat (make sure to remove the .txt at the end).
4. Right-click on cs_textures.bat and click Edit. A notepad window should open.
5. Paste the following into notepad, and save it:
.\steamcmd.exe +login anonymous +force_install_dir ./css_ds +app_update 232330 +quit
6. Close notepad and double-click on cs_textures.bat to run it. This step may take awhile. It should produce a folder called css_ds with a folder within called cstrike
   • If this folder does not exist after running cs_textures.bat, run cs_textures.bat again.
7. Open the game folder for Garry's Mod. Easiest way to get there is from Steam:

8. Open the garrysmod folder, then the cfg folder.
9. Open the mount.cfg file in notepad
10. Find the "cstrike" line and remove the // at the beginning
11. Replace the path in quotes (starting with C:\) with the path to your cstrike folder from Step 6. You can find the path by opening your cstrike folder from Step 6 and clicking the address bar in Explorer.
Your mount.cfg file should look something like this:

12. Save the file and open Garry's Mod.
13. Open the "Start New Game" menu and make sure you can see Counter-Strike Source maps listed