Confused

Question guys! When we exercise we burn calories....are we still supposed to eat the calories we burn off? I'm not used to this! According to MFP, I'm alloted 1600 calories and before I work out I have a meal and a snacks worth of calories left...then I work out and it adds the calories back for me to eat. If I finish the day under my calorie intake....the computer fuses at me! Help!