Creatine does 3 major things for your body:

1) It provides energy to your muscles. This extra energy, called ATP, is especially noticeable in fast or explosive movements like weight lifting or sprinting.
2) Gives an extra “pump” to your muscles. The scientific name is cell volumization, it basically means that creatine causes your muscles to store extra water.
3) Aids in the repair of muscle tissue. Muscle growth is a process called dehydration synthesis. Creatine enhances this process and allows muscles to repair themselves and thus grow more quickly.

The science behind all three of these principals is pretty complex, but I wanted to give a simple high level overview of creatine that anyone could comprehend. If you are interested in all the hard science facts, look for more technical blog posts in the future.