Park Assist is part of the Driver Confidence Package which is available on the LT, Hybrid, and Premier trims. You can find if you have it by opening the trunk, getting to the spare tire area. On the side there by the tire is the Service Parts label. It will have RPO code WPR. If you have that code it is just a matter of enabling it in the MyLink settings.
The audible warning/beeping will only happen if your car is equipped with the park pilot or park assist feature. You can easily find out if your car has that by looking at your rear bumper. If it has 4 small circles on the surface like what is in this picture:
Then you will have warning beeps when you back up. The rear view camera does not provide any audible warning that you are near something, that is done by these round sensors on the bumper.