There's a common little term that we trainers use - "Great abs are created in the kitchen, not the gym". There is a misconception that all you have to do is diet to loose weight, or run 10 miles to look great. What is not understood however, is that you have to have a trifecta of key ingredients to make it all work, and you can't really have one without the others to be effective .
DIET. When I say the word diet, I don't mean restricting entire food groups and starving yourself until you binge on the first thing that reaches your hands. Diet is a mind set, a way of living and looking at food. Instead of focusing on what you can't eat, focus on what you can: whole, natural foods. It's more about the quality of calories you are eating vs the amount of calories consumed. The main bulk of your diet should be coming from vegetables, whole grains, and fruits with meats, beans and dairy making up the rest. Sugars and fats should be used sparingly and as a special treat. You are hungry when your body is looking for the nutrients it needs. If you try to satisfy those needs with a nutrient deficient food - like a doughnut or candy bar - you trick you body into thinking it's going to get what it needs and your body isn't hungry any more. But, this only works for a short time. Your body soon learns that it doesn't have what it needs and becomes hungry again. Once again you eat a food rich in calories, but lacking in nutrients and the cycle starts all over again. If you would have just fed it what it needed in the first place, it would have gotten what it needed, done it's job, and been satisfied with the first bout of calories you gave it.
RESISTANCE. Resistance training is the next step in your formula to great health. It's one of the steps that is most commonly forgotten. As we age muscle atrophy starts to take over our bodies. It is one of the main reasons people lose independence in their aging years, because they are not strong enough to complete even the most basic tasks. Muscle also burns more calories than fat does, making resistance training a key component in weight loss. The more muscle you have the more calories you will burn throughout the day, doing things like I am right now - sitting on my butt in front of my computer. Kinda nice that you can make your body work for you, even when you're not working. You should be doing some sort of resistance training at least three days a week - non consecutive days. It's very important to give you body rest the day after a weight training session. You just spent the workout tearing down your muscles, they need a day to rest and rebuild. This is also where your diet is extremely important, because you need to give them the tools they need to rebuild and become stronger.
CARDIO: This is where you get your fat burning. You just spent a bunch of time building that muscle, now burn the fat off the top of it so you can actually see it. Build up to doing a minimum of 30 minutes of cardio 5-6 days per week. Find something that you enjoy, so it will be easy for you to do it and you look forward to it. Anything that gets your heart rate up and your breathing heavy will do, just enjoy it.
Being healthy and looking fit is a lifestyle, not something you can just work on for a few months and then go back to your original habits. It takes all three of these components to make it work, and a lot of focus and dedication, but you will find as you get into shape and lose weight, that it is so worth it. You will look, and more importantly feel, so much better.