Welcome to the site.
First, read through the stickies at the top of this forum. There is great info there.
They should give you some ideas as far as where to start and what specific questions you can ask to get you on your way.
Here are the most important things that you need to understand to be succesful in losing a large amount of body fat while retaining and even gaining some muscle.
1) The only way you will lose fat is by creating an energy deficit. There are two ways to accomplish this, the first is to reduce the amount of food you eat, the second is to increase the amount of activity you engage in. The best approach is to do both.
2) You need to know what you eat. It sounds obvious, but most people not heavily invested in their physique and fitness unconsciously stuff their faces with all kinds of crap through out the day. Use a site like fitday.com to track what you eat and drink for a week or so to get an idea of what your current diet looks like.
3) Create a caloric deficit by eating a little less food next week than you did this week. A LITTLE LESS FOOD. If you are currently eating 2800 calories, shoot for 2600 calories. As you lose fat you will have to continually tweak this ammount. You know it's working if you're losing weight.
4) To prioritize fat loss over the loss of lean body mass eat plenty of protein and lift heavy weights. Most people on this site will recommend 1.5 to 2 grams of protein per lb of lean body mass. When very obese this can be a hard number to determine, so focus on making sure that every meal you eat has something like 30-40 grams of protein. That would be a can of tuna or a couple of big hamburger patties. A protein powder like Grow! whey (sold on this site) can be extremely helpful in dieting as it allows you to get in a large amount of protein without many extra calories. You can slam a protein shake inbetween meals if you're having a hard time keeping protein high. Small meals are generally bigger than large ones in a fat loss scenario. You will be hungry so many little meals can help you keep from breaking and binging on something you shouldn't eat.
5) Eat your veggies. Fiberous vegetables like broccoli, cauliflower, kale, spinach etc. are high in vitamins and fiber and will help keep you full. Every meal you eat should include at least one serving of veggies.
6) Limit your sugar intake. Many people find it easier to lose weight on a low carb/high fat diet, but even if you do not go this route you should limit your sugar intake to fruit. Fruit juice, soda and other sweetened drinks should be a total no go for you right now. Likewise limit alcohol consumption. If you're in the habit of pounding a couple six packs a couple times a week you're going to find fat loss very difficult.
3) Do not fear fats. Fats did not make you fat, too much food did. Not saying that you have this mistaken mentality, but many people do as the result of decades of bad dietary advice from physicians, schools etc. You should get fat in your diet from sources such as olive oil, avocados, seeds (pumpkin, sunflower), nuts (almonds, walnuts, cashews etc.), meat (beef, pork, lamb), fish (salmon, mackeral, sardines) and whole eggs. Fats and cholesterol play a crucial role in nearly every biological process in your body, they also increase satiety (feeling full), very important on a diet.
In addition to getting your diet in order you will need to increase your physical activity. There are a ton of routines on this website, pick one that sounds fun. You will want something that has you lifting weights in the 3-5 or 8-10 repetition range most of the time in order to maintain strength and give your body a reason to maintain muscle as you diet down.
Make sure that it includes big compound lifts such as squats, deadlifts, overhead press, barbell row and bench press. Starting strength is a very popular beginners program that can include all of these but little in the way of variety over all.
You should probably start out lifting 3 times a week for no more than an hour per session. You should do low intensity cardio every day. 30-45 minute walk in the morning, 30 minutes on a cardio machine after your workouts is a common setup. I personally like hiking for my cardio, much less boring and more strenuous than a treadmill.
That's pretty much it. If you eat right and work out hard on any basic program you will see results. Once you start trying you can develop more precise goals and questions that the people on this board can help you out with.