I have the Front Camera on Lexus IS 350 but have no idea how to use it didn't ever see it turn on either,
Is it for maybe Cruise control?

 

I think what you're looking for is this guy right here. It is part of the 360 (surround view) camera system.



The part in your photo, on the other hand, is used for the safety system and radar cruise control.

 

There should be a button below your steering wheel to the right. On my Japanese is500 it says “view”
press that while in Drive and the camera should show on the screen.

Actually, that camera is in the grille. I’ve no idea about this one.

 

Yes, this is the button. It is on the left because left-hand drive.

 

The windshield forward facing camera is part of the Lexus Safety System.
Check out the various functions it provides on the attachment under IS.
Note that your windshield wipers pass over this area.