1. Install Steam
If you don't already have Steam installed, download it here. If you don't have an account, signing up is easy, and you don't have to make any purchases to play GoldenEye: Source.
Also necessary is Source SDK Base 2007. Steam will install this for you if you don't have it, but you can also install it from the Tools section of your Steam library.
2. Install GoldenEye: Source
Download links for GoldenEye: Source can be found on the download page.
If you downloaded the installer: After the download completes, simply run the installer and follow the instructions.
If you downloaded the zip file: Please follow the steps in this guide.
3. Restart Steam
For GoldenEye: Source to appear in your games library, Steam must be restarted after the installation is completed.
Now that you've made it this far, you are ready to play GoldenEye: Source!
If you encounter any issues, check Client Troubleshooting.