There are several levels and variations of this exercise.
Supermans Level 1 is similar to Bird-Dog but sometimes, one simple change makes a huge difference. As the name suggests, this exercise puts you in a position that emulates Superman while he flies, which also explain why so many levels and variations :) Doing this exercise correctly and safely is simple and requires nothing more than your body and the floor. Well, You may wish to lay down a mat or rug to avoid laying directly on the floor, this is not Sparta :)
This is a great exercise for strengthening your lower back and toning your glutes.
Lie face down on your stomach with the arms and the legs extended.
Slowly, lift your left leg and right arm. Hold 2-5 seconds and back to starting position and alternate sides. Exhale as you lift your arms and legs up off the ground. Inhale, as you lower your arms and legs back down.
Don´t pull. Focus on your back and glute muscles, gently rising as much as you can. Probably you feel easier one side than the other. Don´t worry, there is always a weak side :)