Rotors are always turned off the vehicle. They are put on a lathe and a thin sheet of metal is removed to make the surface smooth again.
No they can be turned off the vehicle.
Are you trying to turn your rotors? I had mine taken off to have the rotors turned only to find out that they are not supposed to be removed.
Remove the rotors and take them to a machine shop for inspection. If there is not much damage they can be turned.
Warped rotors. They need to be removed, turned or replaced.
Your rotors are warped. You need new brake pads and the rotors turned at a machine shop or replaced.
You have warped rotors. Have them turned at machine shop or replace them. Also replace the brake pads.
NO. The rotors will rust overnight if the conditions are right. The rust will be removed the first time the brakes are applied. Yes if the rust has pitted them. Just have them turned on a brake lathe.
Your rotors are warped. You will need to remove the pads and rotors and take the rotors to a machine shop and have them turned. Then install new pads. Make sure you torque the lug nuts to factory specs. Over-tightening the lug nuts can warp the rotors.
You have a warped rotor. Remove the rotors and have them turned at a machine shop or replaced if it it too far gone to turned. Replace the brake pads at the same time.
the rotors
You replace rotors when they get too thin, or are warped. They may be to thin to be turned and still alright to use. Rotors do not "have to" be turned to put new pads on.
Your front brake rotors are warped. They need to be removed and turned true on a lathe. Many auto parts stores offer this service.