If you are trying to lose weight, the best method is simply create a deficit in calories.
3500 calories = 1 pound
In order to lose one pound a week, you'd need to create a deficit of 3500 calories for the week, or 500 calories per day.
Example: 250lb man, 6 foot tall, age 30 would need approximately 3000 calories a day to maintain that weight.
If you reduced your calories to 2500 per day, with no added exercise, you should lose a pound a week.
Now this isn't an exact science, it's all based on averages, etc. Find your caloric need, set your weight loss goal, and find out how many caloires of deficit you need per day to accomplish this.
By adding exercise, you can take the average caloric burn and subtract that as well.
Let's say you need 3000 calories to maintain weight, and you decide that a pound a week is a good ammount to lose, that means on your days you exercise, you can technically add more calories that day and still maintain a 500 calorie deficit.
Building muscle/strength and cutting weight is possible, but if you are strictly focused on building mass, then you want to create a surpluss in calories for your body to grow.
Keep your daily intake somewhere around 40% protein, 30% carbs, and 30% fat. You can even step that up to 50% protein, 30% carbs, and 20% fat, to reduce your fat intake.
Make sure the proteins you are taking in are lean, the carbs you take in are complex, and the fat you take in is low in trans fat.
Successful weight loss doesn't happen overnight, any quick loss typically results in quick regains after you stop.
Bring on the experts to correct me here