Creatine supplements increase your muscles Phosphocreatine stores
Phosphocreatine aids the formation of Adenosine Triphosphate (ATP), the key molecule your cells use for energy and all basic life functions
During exercise, ATP is broken down to produce energy.
The rate of ATP re-synthesis limits your ability to continually perform at maximum intensity, as you use ATP faster than you reproduce it.
Creatine supplements increase your Phosphocreatine stores, allowing you to produce more ATP energy to fuel your muscles during high-intensity exercise.
This is the primary mechanism behind Creatine's performance-enhancing effects.