The dumbbell squat is a great exercise for the quadriceps muscles, especially if performed on a step box, as this will increase the range of movement for the exercise and as such increase the amount of muscle fibers used by your quadriceps.
Not only is this is a very good exercise for toning up the thigh (quadriceps), it will also work your glutes (buttock) and hamstring muscles.
Position yourself with one foot firmly placed on a step box, in order to increase the range of movement for the exercise, however you may decide to simply bend one leg.
Holding onto either a chair, or keeping your hands against a wall, lower yourself down, keeping your back straight and head up.
Remember the one main rule when doing any squat style exercise, is to avoid extending your knee past your toes. Focus on taking your buttocks to the floor, rather than bending your leg.
Avoid going down any further than a 90-degree bend in your leg, as this increases the risk of injury.
The exercise can be made harder by holding onto a suitable dumbbell weight.