The red key is used to program additional keys for the car. The handbook will explain in detail how this is done.
Most (if not all) key-cutters will not cut a blank from the standard back keys to your car, they will only accept the red key.
Once you have the new black key cut, there is a sequence of inserting the red key in the ignition and turning to various positions � and then doing the same with the new black key you want to program.
If you only need two keys for your car � just keep the red one safe, for when you loose one and need another one cut.