How Can I Build My Endurance??

Just run as far as you can, not just til you can't breathe, but til you feel like you might throw up. Then take it easy. Then start again when you can. The only way to gain stamina is to keep practicing and keep pushing yourself over time.

Small weights and a "stepper" might help. Or if not a stepper, I use the bottom stair, to step up onto and back down several times a day. This helps your leg muscles, and small weights would strengthen your back, thus helping your legs, and many other muscles in your body. You'd soon be able to walk further, and increase it a little each day. Brightest Blessings and good luck with your endurance building.

Just keep doing,it has something to do with force.

You need to do slower and for longer. you need to gradulaly build this endurance or fitness. It is important to keep well hydrated and everyday or week push your self a little bit further, you should start with an easy goal and make sure you complete it the next day do it a little faster the next day for a little longer. It will take awhile but it is the only way to build fitness by pushing beyond your current limits. Also you should make a doctors appointment and make sure there is no breathing problems.