Take things slowly. Make a new healthy choice everyday. Drink no soda in a day, the next eat more fruits and veggies. The best advice I can give is don't think of this as a diet. This is not a quick fix, silly gimmick, as soon as I lose weight then I'll be happy.
This is a lifestyle. Say to yourself each mornig: I will drink water. I will opt for a salad for lunch instead of a sandwich. I will eat breakfast. I'll only eat candy sometimes. Etc. Whatever healthy choice you want to make. Whatever suits your lifestyle.
And ask yourself, are you really ready mentally to make a change. Are you committed to the slow, 1-2 lbs a week weight loss? If you are, great! Do it for you. Not ready? It's okay, take your time. You didn't gain it overnight, and you won't lose it overnight.
As for exercise...take it slow. Walk. It's easy and simple. Park your car further away from stores. Walk around the block. Around malls. Incorporate movement into your everyday life. Can only walk for 5 minutes? It's a start. Tomorrow aim for 6. Baby steps here. You can do it. We believe in you.