I want to play with cuss pack but I don't know where to get it and how it works. I hear that gog version have the file but I can't find it, also adult mode in-game ask me a password that I don't have!

It's in the extras section if you browse to the game from your library on GOG's website (see the image). If you're using Galaxy, I have no information regarding it as I do not personally use it.

As to the install of it, read this thread.