how to exercise safely.
Here's a motivating and useful quote: "She urged trainers who work with people with chronic ailments to start slowly with easily achievable goals, build gradually on each accomplishment and focus on functional gains. Over time, a sense of accomplishment, better sleep, less pain and enhanced satisfaction with life can become further reasons to pursue physical activity."
Remember, exercise is not a mean thing the anti-fat people came up with to torture you because you are not pretty: it something you should do because it's good for you. Separate it from the competitions of yore (always losing, feeling uncoordinated, and being picked last made me think of PE as my special torture time) and think about it as something you do with your body for yourself. If you are suffering from depression, make yourself exercise regularly, and just start today. It does, REALLY, help.