To tone your stomach, you need to work on your core muscles. Core exercises tone by strengthening the underlying muscles of the stomach area.

You may think that stomach-reducing exercises only involve pushups or situps, but other core exercises can also tone stomach muscles. You will need to do some aerobic exercise, such as brisk walking, if you want to lose fat in the abdominal area.
Twisted Ab

This exercise targets your abdominal muscles and your obliques. Sit on an exercise mat. Extend your legs and point your toes. Your thighs should be together and your abs tightened. Lean back, with your forearms on the mat. Your fingers should be forward and your palms flat. Lift your right arm over your head, leaving your left arm on the mat. Twist your waist to the left. Return to the center position. Lower your right arm and raise your left arm over your head. Twist your waist to the right.  
Pelvic Tilt Ab

This exercise targets your lower back and your abdominal muscles. Stand with your feet hip-width apart. Keep shoulders down and knees slightly bent. Tighten your abs, then tilt your pelvis forward. Your back should be rounded. Return to a center position. Now tilt your pelvis backward so that your rear end is sticking out. Do two sets with 15 repetitions.
Fitness Ball Crunch

This is a core strengthening exercise. Sit on top of a fitness ball. Feet should be on the floor and spread hip-width apart. Tighten your abdominal muscles and place your arms crossed on your chest. Lean back until you feel your abdominal muscles working. Hold and take three deep breaths. Return to an upright position. Repeat the exercise.
The Ab Bridge

This will work different muscles in the area. Lie on your back. During this exercise, do not press your back on the floor or arch your back. Bend your knees. Tighten your stomach muscles. Raise your hips until they are aligned with your shoulders and knees. Take three deep breaths as you hold this position. Lower your hips and repeat the exercise.
Abdominal Press

Lie on your back. During this exercise, do not press your back on the floor or arch your back. Bend your knees. Tighten your stomach muscles. Bring your legs up off the floor, first one, then the other. Your hips and knees should be bent at a 90-degree angle. Put your hands on the top of your knees. While using your stomach muscles to pull your knees toward your hands, push your knees in the opposite direction with your hands. Start at the beginning and repeat the exercise.