My best advice is to throw on your gym clothes and shoes, put on your headphones, open up your front door, and take off jogging. Don't worry if you only make it 10 feet before you have to start walking- just keep moving as fast as you can. 10-15 minutes is all you need. Do this 3-5 times a week to build up time and distance.
In the mean time, surf the menus and nutritional information online for your favorite fast food places. Find out the healthier choices on the menu (most fast food establishments are expanding their healthy offerings these days). This way when you get stuck eating fast food, you know what's best for you.
Then go to the store shopping as normal, but don't just look at what you're buying, look at the choices around it. Most items have organic, low fat, non fat, low sugar, no sugar, etc. alternatives. Start substituting some of these guys into your cart and over a short period of time, you'll find out what you like. Pay attention to the nutritional info on the foods you eat. By doing this, you will begin to gain a sense of what's healthy and what's not and will have a better idea of what to order at restaurants when you don't have the info in front of you.
The rest of it is automatic. Within a short amount of time, you will feel really good and your body will crave exercise and healthy food. If you want more tips and/or motivation, I lost 80 Lbs and wrote an e book about it. You can read the entire thing for free at my blog at .
*And don't worry, I won't try to sell you anything. I was in a bad spot with my weight at one point and I know how annoying it is being given advice online in an attempt to sell a product.
GOOD LUCK!