i understand that cardio is good for the heart and for burning fat obviously. I just dont understand how it works though... for example, lets say you do a light run for 20 mins and burn 300 calories, now if you eat 5000 calories a day wouldnt that just subtract from the calories you ate that day meaning you dont really lose any fat? therefore you just lose gaining size that night cause you've lost the extra calories?

I know there must be a explenation for this as i said i dont understand how it works. Im just curious cause im bulking at the moment and i dont want to lose anything from keeping me growing at max, although id like to shed some fat too. In which case should i do cardio although im bulking?

Im talking about all this whilst on cycle, not natural.