There are 2 common approaches to exercise for weight loss...
1) Exercise to burn calories (and fat if you know what you are doing)
This is usually some form of cardio and usually for at least 1 hour. The down side is that your metabolism hasn't changed, so you have to exercise every day to maintain the daily calorie usage.
2) Exercise to build muscle (or regain lost muscle) and burn more calories 24/7
Muscle is metabolically active even at rest, so by increasing muscle mass you increase your daily calorie requirements. The workouts are usually less than 30 minutes, and ideally you have a rest day between each workout - while the body is repairing & building muscle on your rest days you are still burning calories.
I recently joined an online exercise & weight loss program where I do resistance training 3 times per week, and the workouts rarely last longer than 15 minutes, and I have seen incredible results! As I have become stronger and fitter I have found myself wanting to do more exercise, so I now do additional cardio on my rest days. This is easy for me to do as I take my dog for a walk every morning - All I do is increase the intensity (brisk walking or jogging), and I am really enjoying it.
To maximize the effects of the exercise make some simple adjustments to your diet - Cut out as much processed foods as possible, increase your fiber intake (fruit & veg), and buy organically if you can.
Hope this helps.