The human body stores most of its access energy intake as fat. These stores of fat represent an amount of energy better known as a calorie. These calories can go further to represent energy intake as well as energy output. Quick recap: food in = calories and energy out = calories. Ok, are you still with me?
According to the American College of Sports Medicine, it costs roughly 3500 calories (to make or burn) per pound of stored fat. Now lets put that to use. The human body will expend about 100 calories per mile, walking or running. This means it will take the average person 35 miles walking or running (alone) to burn 1 pound of fat.
Add some activity variety to your routine and avoid an exercise rut. A rut or recurring state can increase risk of injury but also lead to a progress plateau, a state of no gains. Nobody wants that. Walk some days (3.0+mph) and run on the others (5.0+mph) at least 5 days a week. Increase your distances every two weeks by .25 - .5 miles. Add at least two days a week of strength training and you're on your way.
You can start with .5 - 1 mile and work your way up from there. Remember consistency is the key to achieving any fitness goal.