A hydraulic park lock uses brake line pressure to hold your brakes. Typically, to install this, you cut the brake line that leads from your master cylinder to your rear brakes and install this in that brake line. To activate the park lock, just push the brake pedal down with your foot, then push the park lock button down. To deactivate the park lock, tap on your brake pedal with your foot and it will release the park lock.
This universal park lock is great for highly modified off road rigs where a long travel suspension or aftermarket axles prevent you from using a conventional cable-type parking brake.