How do you burn more calories than you consume?

I'm really confused. I heard to lose weight you have to burn more calories than you consume. I've looked up how many calories you burn while dancing and it said you burn 150 an hour. I want to go on a 1200 calorie diet but I feel like I can't lose weight if I only burn 150 calories. Can someone clear this up for me? I want to try to lose 2-3 pounds a week....