It is really simple to install source metamod on your game server. First you need to download the latest version of sourcemm & metamod.vdf file from their website Metamod: Source for Half-Life 2. After you download sourcemm click on the link "make your vdf" to create the metamod.vdf file for the game server you are installing metamod on. For my example below i did the manual installation of metamod on my counter strike source game server. After unzipping the files you are going to see a folder called "addons" in that folder there's another folder called "metamod" inside the metamod folder there's a file called metaplugin.ini
addon/
addon/metamod
addon/metamod/metaplugin.ini
addon/metamod/bin
addon/metamod/bin/server.dll
addon/metamod/bin/server_i486.so

Open the file called metaplugin.ini with wordpad or notepad to add a line for the admin mod you are using in your server. The line that you are going to add here is the metamod name for the admin mod you are using. Since my server is using mani admin mod i'll add mani_admin_plugin_mm. If you're using sourcemod the line you need to enter for the metamod is sourcemod_mm. Now we need to add the file path to the mani_admin_plugin_mm or sourcemod_mm.
Mani mod file path: addons/mani_admin_plugin/bin/mani_admin_plugin_mm
Sourcemod file path: addons/sourcemod/bin/sourcemod_mm
Like the file says you do not need to add the last part of the name _i486.so or .dll
Since you are going to use metamod:source with mani admin plugin you do not need the files mani_admin_plugin.vdf, mani_admin_plugin_i486.so, mani_admin_plugin.dll that are in the addons folder.
Once done upload the file to the metamod folder with the rest of the other files.
You need to connect to FTP and find your way to the /cstrike folder of you counter strike source server. Once inside of the /cstrike folder check to see if you have an addons folder like the picture above. If you don't have an addons folder create one or upload the one that was inside the zip file.
Now you need to download the Gameinfo.txt file that's inside of the /cstrike folder and add the following line.
Code:
Gamebin |gameinfo_path|addons/metamod/bin
Add the line above inside of the { brackets } where the other game path are.

Add the line the same way it looks in the example above then save the file and upload it to the game server.
Restart the server...