As has been said, what you need to do is ride. Your story is an old one. Some fat person decides to become an athlete. Hah! My first ride was about 15min and I got a mile down the road, if that. My butt hurt so much I never even got far enough to get out of breath. I couldn't get up the first little hill I tried. Had to turn around half way up and it was only 300 feet or so. Now I do 8 mile hills with 10% grades. Your best bet is to simply ride for as long and hard as you can and combine that with decent food in reasonable quantities. This forum is filled with success stories that started just like you. Welcome aboard and keep it up.