The gluteals — your butt muscles — are the largest and strongest muscles in the body. Their function is hip extension, or driving the upper legs backward. I cannot overstate how important it is to make sure these muscles are getting their workout. Activities that engage this muscle group include walking, running, jumping, and climbing. Lunges, leg lifts, and squats are all great for exercising the glutes. Here's the lowdown on some of my favorite squats.
Traditional squat (good if you're a newbie): Stand with your feet hip-width apart, with your weight on your heels. Keep your abs tight and your shoulders squarely over your hips. Sit back and down as if you were going to sit on a bench. Keep your back straight. Then stand up, straightening your legs, and repeat.
Sumo squat (pictured above, good if you're a little more advanced): Place your feet as wide apart as you can and point your toes outward. Lower your body until your thighs are parallel to the floor. Hold for a beat, then exhale and press back up to the starting position. Repeat. This squat modification places a greater emphasis on the inner and outer thigh muscles.
One-leg squat (good if you're a hard-core exerciser): Stand with your weight balanced on your right leg. Lift your left foot an inch or so off the ground. Keep your head up, and don't lean forward; abs stay tight, and the right heel stays on the ground. Don't let the knee extend over the toe. Slowly lower yourself as far as you can comfortably go. Exhale and stand up straight, still balancing on the right leg. Continue for a full set on the right leg, then switch to the left leg and repeat. This modification requires tremendous balance and allows you to strengthen each leg.