[Old and Slow]

If you start out from scratch with a fresh, new Windoze CSGO server, you will have something like this:

...[steamcmd install directory]
...+...csgo
...+...+...bin
...+...+...cfg
...+...+...maps
...+...+...(more)

The csgo directory will have all of the *.vpk files, a bin directory, and a cfg directory. There is no addons directory initially. If you take the MM:S zip file (mmsource-1.10.0-windows.zip), it will have the addons directory as the top level. Unzip that file into the csgo directory - you should now have an addons directory along with the stuff just mentioned:

...[steamcmd install directory]
...+...csgo
...+...+...addons
...+...+...bin
...+...+...cfg
...+...+...maps
...+...+...(more)

In the addons directory you should now see a metamod directory and a metamod.vdf. This should be all you need to get the server running with MM:S.

The VDF file should look like this:

"Plugin"
{
	"file"	"addons/metamod/bin/server"
}

That should work for any HL2-based server. For CSGO, this will also work:

"Plugin"
{
 "file" "../csgo/addons/metamod/bin/server"
}

Now to test it: From the install directory (the one above the csgo directory), make a batch file (run_csgo_dust.bat) that looks like this:

srcds -console -condebug -port 27015 -norestart -game csgo +game_type 0 +game_mode 1 +mapgroup mg_bomb +map de_dust

Assuming that the server starts, you should get a command window that is the server console.
You should see: VAC secure mode is activated.

type: plugin_print
you should see:

Loaded plugins:
-----------------
0: "Metamod:Source 1.10.0"
-----------------

Now type: meta list
you should see:

No plugins loaded.

It is similar for Linux, you will need a different MM:S file (mmsource-1.10.0-linux.tar.gz) and the start command will be srcds_run instead of srcds.

Exit the server by typing: quit

I hope that helps.