For someone who has not exercised on a regular basis ANY cardio activity for 20 minutes or longer several times a week is a good start. Work up from there to activities that will raise your heart level to 80 percent of max for your age but if that’s not feasible, just keep walking (go up and down the stairs at work). Add some weight and resistance training if you can…use isometrics if not.
Anything is better than nothing….