These marks indicate the four corners of the pet-door frame as well as the locations for the frame screws. Start along the bottom, then cut along the sides, and finish with the top. Drill pilot holes through the door at the points you marked for the frame screws. All that's left is teaching your pet to use the door. Try using a snack to coax him or her through, but don't push.
Most pets require less than two days to learn how to use a pet door.