The entire universe is composed of these five elements. They are interdependent and each is controlled by another. Metal can only be melted and forged with great heat. Fire is controlled by Water. Nothing will put out a fire as fast as water.
Water is controlled by Earth.
We dig canals in the earth to irrigate fields or build dikes to keep out or absorb water. Earth is controlled by Wood. Trees and their roots hold the soil together and get their nourishment from the earth. Wood is controlled by Metal. Even the largest tree can be felled by the metal blade of an axe.