Learn the forward undulation, the most basic move. Begin with your right foot slightly in front of your left. Stand on the balls of your feet with your heels approximately 2 inches off the floor. Keep your arms at shoulder height, with the elbows bent at a 90 degree angle and your shoulders back.
Rock forward on the right foot and back on the left. Use music with a 4/4 rhythm and step on your right foot on the 1 and your left foot on the 3. Continue to rock forward and back to this beat until you feel comfortable doing the move with your heels off the floor.
Lift your chest on the 1 as you step with your right foot. Think of this as though you're stepping on the pedal of a trash can and your chest is the lid that pops up. Let your chest drop on the 3. Make the chest lift come from the diaphragm. Keep your shoulders back and down so you don't use them to do this movement.
Add a belly roll as your left foot comes down. Contract the diaphragm and "roll" the move all the way down the belly to the lower abs. Resist the temptation to do this move with the spine and focus on keeping the roll entirely in the abdominal muscles.
Relax the abs and lift the chest again as the right foot touches down. Think of an undulation as a figure 8 that you make with your torso while your feet keep the beat with the rocking motion.