Abdominal crunches or more commonly called just crunches are a staple exercise.  You will do a lot of them and they target your abdominals very well.  Pretty much every other abdominal exercises is a variation of this one, so learn to enjoy them.  Feel the burn.

Starting Position

Lie on your back, hands near your ears or crossed on your chest.  Do not lock them behind your head or use them to grab any part of your face, hair, ears or anything else you can find.  Bend your legs, keeping your feet on the ground, forming about a 45 degree incline from your pelvis to your knees.

Performing the Exercise

Roll forward lifting your shoulders off the ground.  Focus completely on contracting your upper abs.  Hold for a second at the peak of the contraction and then lower your shoulders back to the ground, lightly touching them but do not completely relax, then contract again lifting up.  Continue for the desired number of reps or time.

Tips

Biggest mistake and the one that will cause you the most pain is allowing your chin to touch your chest when you lift your shoulders off the ground.  Doing so causes strain on your neck and back.  Aim to keep a space the size of a tennis ball between your chin and chest the whole time.  It often helps to look up instead of at your knees.  Your head has a tendency to follow your eyes.