1. Commit!
Exercise is a commitment so set aside one hour each day that you absolutely will not let anyone distract you or take it away from you. That one hour is yours. Claim it!
2. Find your exercise of choice.
This may take a while, but you need to try different things to find out which one you like the best. Some people are swimmers, some people are runners, and some people are bikers. Find out which one you like the best and build on that first. You don't have to be good at it, you just have to like it enough to keep working at it to get better.
3. Set goals.
Today I'm going to run to that tree and walk for five minutes and then run to that stop sign and then walk for 3 minutes and then run to that bush and then walk for 3 minutes, etc. Before you know it you'll be running the entire route if that's the exercise you choose. You can do the same thing with swimming and biking.
Once you've mastered the cardio you will find that it becomes a mental game. You'll know it when it happens and you'll be ready to move on to something else, but for me cardio will always take precedence over any other form of exercise. You can incorporate working out with weights into it eventually, but for now just concentrate on working up a good sweat.
I wouldn't necessarily worry about dieting right now. Eating healthy is important, but right now you're just trying to get your body used to moving and working muscle groups that haven't been worked in a while. I guarantee you that after you've worked up a good sweat running, swimming, or biking for an hour the last thing you'll want when you're done is a cheeseburger and fries. Mostly what you'll want is a big drink of water and to sit for a few minutes.
If you choose running, look for a local 5K and start training for that. Make that your goal. There is a wonderful app called Couch to 5K that will get you there.
That's all I have for now, but I wish you the best! You can do this! Own it!