I'd recommend just start walking outside and get some fresh air. If you want to try running, you could download a Couch to 5K app and that starts pretty basic with 8x 1 minute runs with walking breaks in between. If you don't have a pair of running shoes, I'd get a pair that you can use for walking and running. Elliptical or stationary bike is fine too. I'm not to familiar with programs for those but you could try 10 minutes a day and gradually increase.