Instructions
Download the ZIP file that contains your plugin from the plugin author, or from a plugin repository.
Double-click on the ZIP file to open it and view its contents.
Open Windows Explorer by right-clicking on the "Start" button on your game server, then clicking "Open Windows Explorer."
Browse to the "C:\Program Files (x86)\Metamod\Plugins" folder in Windows Explorer.
Left click on the .so file in the ZIP file and drag it into the "Plugins" folder in the Windows Explorer window.
Restart the server (that is, either physically restart the server or restart the game server application) to apply the plugin and start it in Metamod.