Hi Mridula,
To reduce fat and build muscles you need to of more of cardio training exercises like running, swimming, jogging, brisk walking, etc. You need to do these exercises for atleast some 45 min daily or minimum 5/week for better results. This type of exercises will help you to reduce your body fat, Include weight training exercises like lunges, squats, push ups, crunches, reverse crunches, etc. We need to do these exercises so as to tone up your body and so these exercises every alternate days for 15 min.