Does doing a lot of exercise in a day help to lose weight?
Exercise will help you lose weight any time you do it. However, only regular, sustained exercise will be effective in significant weight loss. Regular exercise, aside from simply burning calories, raises the metabolism - which in turn burns more calories over time.
Keep in mind the need to eat healthy foods with enough calories to keep you going, but 200 - 300 fewer than your body will need for the day. Typically, a 1500 calorie diet is a good place to start. Dropping below 1500 calories may cause you to lose weight, but it will also cause you to lose health!