The brain is the most complicated organ in the human body. The brain is composed of several parts that work together. The brain is responsible for everything that we do, including breathing, thinking and feeling. It's divided into two parts: left brain and right brain. The left brain is in charge of logical reasoning, while the creative side is handled by the right brain. The majority of people use both sides, but there are some who are left-brained and others right-brained.