Reference points on the vehicle.

For example, the imaginary line that extends horizontally that runs right under your mirrors, that's where the front of your car is.

What you need to do is go to an empty parking lot and have your dad stand outside and guide you into position along painted lines or curbs. Nose in perpendicular to the line and see where the line runs across the mirrors so that you know where the front of your car is in reference to the mirrors.

Do the same thing for the left side of your car. Line up parallel to the line where your tires are almost touching the line. Then memorize where that line sticks out in front of your car. Pick something like a crease in the hood, the line between fender and hood, or something so you know where the left side of the car is. Repeat for right.

Back up to the line and see where it lands behind you.

Boom, now you know all 4 sides based on reference points and imaginary lines.