When first starting after living a sedentary lifestyle, setting up a workout regime seems so overwhelming let alone doing it. Start with dedicating 10 minutes to cardio and go from there. If you made it to the 10 minutes and still feel great, go another 10 minutes and so on. If you gave all that you can and are exhausted, then you can stop knowing you fulfilled your goal of 10 minutes of exercise.
I find this technique really helps me- I get motivated to workout as its "only 10 minutes" but always surpass my goal and exercise much longer.
Its a great way to get started, and once you have built up momentum and know you can do more you can set bigger goals.