can someone tell me what that Green Light i can turn on and off on my rear view mirror is????the manual says nothing about it

 

That is a dimmer for driving at night. if you turn it off and look at the headlights of other cars behind you and then turn it on you will notice a very significant difference. This way vehicles behind, there headlights wont be blinding to you.

 

The little green light is the 'on' indicator for the auto-dimming rear view mirror. You can turn it off, but the mirror won't dim if someone comes up behind you at night with their headlights on.

 

Honestly, the dealer should have explained that to you when you picked up the car. All dealers should go through all options of the car and explain how they work.