The squat is one of the best exercises you can do to engage your glutes, and using a chair helps to ensure you use a full range of motion with great form.
How to do it: Stand in front of a sturdy chair with your feet slightly wider than hip distance apart, holding a dumbbell in each hand. Bend your knees, shift your hips back and pretend you are going to take a seat. Keep your weight in your heels and don't let your knees extend past your toes. Lower down until you are almost touching the chair, and then stand back up.
Form tip: Don't lock your knees when you stand up—always keep them 'soft'.