I think working out is something you either love or don't love. I love it. Having this silly condition crimps my workouts, but the docs tell me it will be fine.
Find something you like. Whether it is walking, jogging or riding a bike, it takes a while to get there. An old running book I had talked about the "Gate at 5 miles"; the theory of the author was that if you could work up to 5 miles, after that it was easy.
I believe. Once you can run 5 or 6 miles, it is relatively easy to work up to running full marathons, which are 26.2 miles. I can't really run that much any more because of knee surgery, but I started riding a bike last year and it was similar. Until you can maintain a decent pace for 45 minutes to an hour, it isn't much fun. Once you can, it is fun and you can gradually increase to almost anything.
Before my recent diagnosis of having a 5 cm ascending aorta, I was training to ride a bike across the state of Georgia in a one week ride. I rode 150 miles in 2 days for MS in April. Then I got my bad CT news and had to back off.
For a couch potato, I would say to find something you like to do. Give it a couple of months. Make some goals. Work up to them. At some point, it really, really becomes funs. I can't wait until they fix me and I can start working up my distance on the bike. Imagine riding a bike 50 or 75 or even 100 miles at a time; what would you see? How far could you go? How proud would you feel for accomplishing that?
Get off the couch and go for it!
John