I want to play a gamemode in singleplayer...

I downloaded this: http://www.garrysmod.org/downloads/?a=view&id=75935
i wanted to play multyplayer, but i cant connect to the server for some reason, so how do i play it in singleplayer (I know its meant for multiplayer BTW)

How do i play it in singleplayer?

You can’t, it’s just all the clientside files. It would be pointless playing Sassilization in singleplayer anyway, it’s a multiplayer gamemode.

Most of the files required to play the game are private files, only accessible when you connect to the servers with the files, and are undownloadable. The person who uploaded that only did so so people didn’t have to download all the files when they connect to the server for the first time.
Also, don’t connect directly to the Sassilization servers, connect through the lobby at:

Lobby.Sassilization.com:27015

Sassilization is pointless singleplayer, you literally can’t do anything. Besides the serverside files aren’t released so you can’t play it even if you wanted to.

I don’t understand why everyone wants to play lobby games in single player. They suggest this without any thought of how there would be no gameplay at all.

It’s like playing RP by yourself, which already has no real gameplay.