Creatine is a compound that can be made in our bodies or taken as a dietary supplement.  Here is the chemical makeup of creatine -

Creatine is made up of three amino acids - Arginine, Glycine and Methionine. Our liver has the ability to combine these three amino acids and make creatine. The other way we get creatine is from our diet.

This varies based on the amount of muscle mass you have and your weight. On average a 160 pound person would have about 120 grams of creatine stored in their body. It is believed that 95 - 98% of the creatine in our body is stored in our muscles. The remaining 2 - 5% is stored in various other parts of the body including the brain, heart and testes.

1. Provide additional energy for your muscles

In your body you have a compound called ATP (adenosine tri-phosphate).
 

    

Adenosine Triphosphate (ATP) is the primary energy source found in all living things. ATP fuels most cell activities, including muscle movement, protein synthesis, cell division, and nerve signal transmission. In this computer graphic representation of an ATP molecule, the three phosphate groups are shown in orange. ATP's chemical energy is stored in its phosphate bonds.
Francis Leroy, Biocosmos/Science Source/Photo Researchers, Inc. 

Think of ATP as an energy containing compound. What is important to know about ATP is that the body can very quickly get energy from a ATP reaction.  When you are doing an intense quick burst activity - such as lifting a weight or sprinting, your muscles must contract and need a quick source of energy. This immediate energy comes from ATP.

When your muscles use ATP for energy a chemical process happens where the ATP is broken down into two simpler chemicals ADP (adenosine di-phosphate) and inorganic phosphate. This process of ATP turning into ADP releases the energy which gives your muscles the ability to contract. Unfortunately, we do not have an endless supply of ATP. In fact, your muscles only contain enough ATP to last about 10-15 seconds at maximum exertion.

Here is where the creatine comes in - or more specifically the creatine phosphate (CP). CP is able to react with the ADP in your body and turn "useless" ADP back into the "super useful" energy source - ATP.  More ATP in your body means more fuel for your muscles.

2. Cellular Hydration of your muscles

This is the process of pulling fluid into the muscle cells and thus increasing the volume of the muscles. Creatine has been shown to pull water into your muscle cells, which increases the size of your muscles.

3. Buffer Lactic Acid build-up

New research has shown that creatine can help buffer lactic acid that builds-up in the muscles during exercise. This leads to that nasty burning feel you get in your muscles. Scientifically it is a complicated process - basically the creatine bonds with a Hydrogen ion and that helps delay the build up of lactic acid.

4. Enhances Protein Synthesis

There is some data to indicate that creatine helps put the body in a more anabolic state where protein synthesis can occur. The more protein synthesis - the greater the muscle gain.

The average human has between 3.5 and 4 grams of creatine per kilogram of muscle. Once you use up the creatine in your muscle you have to rest your muscles and wait a while before you can exercise the muscle again. Studies have shown that the human muscle can store up to 5 grams of creatine per kilogram. Excess creatine is eventually converted into the waste product creatinine and excreted from the body.

It very important to know more research needs to be done.