Works by achieving higher stores of phospho-creatine in your muscles. This then allows you to train harder in gym and cause more "Stimulus" that makes your muscles grow.
Usually comes in a powder form. Creatine will help provide the energy to lift the last few reps on a set of 8-12, it will not make you stronger in a 1 rep maximum situation, but can let you last longer and lift more reps at a given weight over 4reps.
***I do not recommend paying inflated prices for "extra" ingredients in a protein shake. Again just a simple Creatine Monohydrate or Creatine Malate will be sufficient. It is also recommended that when you are using creatine that you do not drink alcohol, as it has the opposite affect .
For dosage and loading principles look for the AIS NUTRITION FACT SHEET: CREATINE, as it sums up the recommendations perfectly. http://www.ais.org.au/