Start with some simple exercises each day, start out with just little things you can do like a small short walk around you neighbour hood block or something shorter if you live on a large block. Gradually increase the distance and the pace you walk at and one day try slow jogging for maybe the last half of your trip. Combine this with regular healthy eating, this means ABSOLUTELY NO junk food, not even a potato chip, i know this is hard to do but just think of the end reward you ARE going to achieve one day shortly. If you think 1 bag of chips isn't going to hurt and no one will know about it then you are only cheating yourself, so it's not worth it, is it.
Life can throw us some challenges, but hang in there. There's no need to have negative thoughts, take each day as it comes and think of it as a small step towards your positive future. You'll get there, don't be jealous of others because they may have things that you wish you had, heck for all you know they could be wishing they had some of the great things you have in your life. A good way to keep positive is find something (not eating junk food!

haha) you get alot of enjoyment and pleasure out of and do it as often as you can. If you can find an exercise that gives you enjoyment and pleasure than you are shooting two birds with one stone really. Always keep your head up! after all, life is great!