People who exercise have different requirements because the more you exercise, the more you have to eat to sustain that level of activity. This also applies to casual exercisers, but it may not apply to you if fat loss is one of the reasons you took up weight training. In this case, you need to create an energy deficit; which means that the energy (or calories) you consume in food is less than the energy you expend in exercise and daily living. Your weight training, in this case, is to assist with fat loss while attempting to maintain muscle.
One of the most misunderstood areas for new bodybuilders is nutrition. I talk to guys all the time that have no idea of their daily calorie intake, their daily protein intake, their carbohydrate intake. They have no idea of what types of foods they should be eating, or when they should be eating them. They don't know what supplements do what and what they should using. Let me refer readers to some of my other articles that detail these areas.