I have a couple ideas for you.
1. Get started, doesnt matter what you do, but do it on a schedule. Make it a habit. Start with walking 5 times per week if you must. 3 to 5 miles, brisk pace. If you aren't sweating at least a little bit, you aren't pushing it hard enough.
2. Watch what you eat. Diet will help you get in shape.
3. Find an accountability partner, someone who will tell you to get off your couch and get your exercise in for the day.