What is creatine? Creatine is made up of three amino acids - Arginine, Glycine and Methionine - which our liver combines to make creatine. We get it in our diet from meats and fish, but to boost your intake and get a training effect, most people take it as a supplement.
How does it work?
Without getting into the chemistry, from a user's point of view creatine works by enabling you to work harder, particularly at the back end of a set or workout - the part where you're exhausted and usually quit. By helping you squeeze out an extra couple of reps it encourages muscle growth.
Which type of creatine should I take?
Although there are various types on the market, research demonstrates that basic creatine monohydrate powder is highly effective. There are various formulae that mix creatine with other substances (usually some form of carbs) to deliver it to your system more effectively, but they are quite expensive. You can achieve a similar effect much cheaper by mixing it with a little Gatorade or fruit juice, or eating a banana with your creatine drink.
There are research papers showing additional benefits from taking creatine with a variety of nutrients including protein, glutamine, and glucose. Ultimately you have to choose what works for you based upon your normal nutritional requirements, and what you can afford!