Congratulations for committing to your health! It may seem like a significant effort at first, but the more you do it, the easier it will become.
It may be very beneficial for you to seek the help of a personal trainer to assist you in setting up an appropriate exercise plan. Even if you just meet with him or her once or twice for an initial consultation. He or she will be able to help you safely establish your goals and exercise routine. Here is the link to find an ACE certified personal trainer in your area:
Since it sounds like you are new to exercise, finding a mode of activity that you really enjoy is very important in order to maintain your commitment. If you are feeling unfocused at the gym while on a stationary cardio machine you may need something a bit more interactive. Perhaps a group fitness class would be something fun to try. In your area or at your gym there may be a variety of group classes such as boot camps, zumba, spinning, or perhaps an adult sports league. You may want to talk to the gym’s fitness manager to check into what your facility offers.
To begin with 15 minutes of cardiovascular activity is a great starting point! Depending on your frequency of training, you may be able to increase each session by 10%, or 5-10 minutes every other week over the first month or two. Working your way up to 30 minutes at a time is great goal for general health, with 60 minutes per session being more appropriate for weight loss.
Here is a link to help you find a variety of exercise routines to fit your needs:
Good luck, and keep up the good work!
Bryant and Green. (2010) ACE Personal Trainer Manual (4 th Ed) . San Diego, CA.: American Council on Exercise.