How does the rear parking brake work on 04 Hyundai Elantra gt with disc brakes?

If it's the same set-up as a 2005 Hyundai Elantra GT with disk brakes all around (my car), then it's pretty simple. When you pull the e-brake lever, it tightens 2 cables which pull individually on a lever that is attached to each caliper. This lever turns the piston inside the caliper which tightens the pads on the rotor. Thus, your vehicle stays in place (theoretically).

If your cable is too loose or your pads are too worn, then the parking brake will not engage. Or in my case, if both brake cables rusted to hell and then snapped, it won't work either.