This exercise develops the hamstrings, the glutes and the quadriceps.
By all means you have to learn to perform this the right way, otherwise you will overburden your knee joints.
Stand straight, step one big step forward and with your straight leg slowly lower yourself into lunge position so that your ankle, knee and hip form a square. Pay attention that during the exercise the knee should not go beyond the toes, your torso should be straight all the way and in an upright position. As soon as you lowered yourself into this position, you should use your leg to straighten yourself that is step back to the starting position. Step forward with your other leg and repeat with alternate legs. If your thighs are strong enough then you can make the exercise harder with two dumbbells; simply just hold them next to your body and pay attention that you should not swing them.