Squats - Machine

Sit in the middle of the seat with your feet hip width apart and parallel. Keeping your hips, knees, and ankles in one line, engage your abs and press your back against the back pad.

Lift the weight, straighten your knees without locking into the knee joint, then slowly bend your legs to the starting position.

Sometimes these machines have different names. Basically they lead you through good form for a squat to strengthen the major leg muscles.

Thighs 

Hips  Lower Legs 

Rectus femoris, Vastus lateralis, Vastus intermedius, Vastus medialis, Gluteus maximus, Adductor magnus, Soleus

TIP: Watch your knees closely to assure they do not lean into or away from each other. Try to angle your knee over the center of your ankle, about towards the 2nd toe.