How to make working Google Now Offline and add command ?

[UnReal']

Hello !

I have an Android Head Unit in my car and Google Now is really good to use while driving.

But the problem is that I don't have connection everywhere and wanted to ask how to use the offline mode , and use special command like 'Ok Google play "SONG" from "ARTIST" '.

I tried Tasker but I don't understand everything... If anyone can help me