Calories in vs Calories out. Get your BMR (Basal Metabolic Rate) then Multiply that by your activity factor. From there you should get a numeric value for the calories your body consumes in a day. 1 lb has 3500 calories in it, so a general guideline is to eat 500 calories less per day than your calculated value. That way you lose 1 lb a week.
Working out and cardio together not only allow you to lose weight, but muscle itself burns more calories, so as you ramp up on the weights and build muscle, you'll be burning more calories at rest just from being more muscular.
Finally, EPOC is exercise post oxygen consumption, or the amount of oxygen you use after exercise. The longevity is increased when doing cardio after weightlifting. What this does is not only do you burn calories while doing cardio (be it running/sports/machines), but you also burn calories after the workout for longer than cardio alone
Hope this helps
