Protein is made of long chains of amino acids, which are the building blocks of muscle. You need protein to maintain current muscle and to create new muscle. Most of your protein intake should come from food but as you do your research you will find that it becomes difficult to get your daily requirement of protein without getting too much fat. Protein powders are perfect to help you increase your protein intake without excessive calories, fat, carbs etc. AND... its generally much cheaper than chicken or steak per gram of protein.