Begin with a daily walk of at least a half an hour. Gradually increase to 3 miles a day, and then gradually get the time for the 3 miles down to an hour or less, you can start doing light weight work 3 days a week also.
It is important not to push too fast on progression. An increase every 2 weeks is plenty. Be sure to keep your caloric intake to 1500cal/day or less if you want weight loss.