I would give you two alternatives of training. Note that in either of the two options you can practice different types of aerobic exercise preferably running, riding a bike or elliptical machine.
The first is recommended for beginners and consists of a session of 5 intervals of 4 minutes each row to complete all 20 minutes of exercise. Each range will consist of three minutes of low to medium intensity followed by a minute of high intensity. These intensity changes elevate your oxygen consumption post-exercise which results in burning more calories at rest after exercising.