Hi Pooja,
I agree with Bhavya. Running is a great cardio sports which requires good endurance of our heart and lower body muscles so as to cover more distance. So we need to work more on to increase your endurance. To increase endurance we need to do cardio activities like Jogging, Swimming, Skipping ,Brisk walk, etc. will help improving our endurance. But if you are planning to run for a marathon then we need to start preparing for it slowly like first starting with brisk walking for a month then moving to jogging, and later to running so it will help to slowly get adapted to running and so will help improving performance. Also look for the posture while running so as to have relaxed breathing. While running we should have cadence breathing in which we breath in after 2-3 steps and breath out after 2-3 steps. Keep your shoulders relaxed and a little bit retracted so as to take in more oxygen in lungs.