I sit at my desk and do bicep curls lifting my coffee cup from my desk to my mouth. Additional exercise from dunking a cookie into the coffee with my other hand. I've lost 17kg in 6 months on this fitness regime. And no, I'm not exaggerating, just leaving out the context I still have about 4-5kg left to lose to get down to my goal weight, so thats ... er ... 53 litres of coffee and 20 pounds of cookies.
It sounds like you should start with basic calisthenics to get your body in shape for doing any exercise. Basic calisthenics would be jogging/running, push ups, sit ups, jumping jacks, and stretching all limbs and muscles. Once you can do 30 of each exercise and run half a mile then start weight training. I only recommend this because if you're asking then your muscles might not be able to handle an immediate workout. You wouldn't want to hurt yourself.