Many, many people have done exactly what you're wanting to do. It works. You'll need a sturdy bike. Probably a mountain bike is a good thing to start with. Talk to your local bike shop. You don't want a department store bike - it won't hold up. Buy good bike shorts, and decent bike shoes, too. You won't need or want clipless pedals to start with. Start by just riding a little. Around the block is good. Very gradually increase your distance. Try to ride 6 days/week. Don't push hard, just ride. It's time in the saddle that does it. Don't reward yourself with food for riding or try to eat back the energy you expended. That's really easy to do. Enjoy riding! It's really fun. The more you enjoy it, the more likely you'll be to do it. So explore on the bike. Go places you don't go in a car. Look for quiet roads. Be curious, have fun. And good on you.