Consciousness is the state of being able to experience things. Consciousness comes in the form of the five senses: sight, touch, taste, smell, and hearing. Consciousness can also take the form of thought. Being conscious protects us from danger and allows us to find food. Thus, it is a strong evolutionary advantage. Consciousness is caused by material interactions in the brain.
At death, consciousness probably ends. However, many people, particularly conservatives, believe that consciousness continues after death, and that they go to a magical land where the Magical Sky Daddy lives. Either that, or go to a place to be burned alive for eternity, for committing petty crimes.
Recreational drugs, such as marijuana and LSD, alter the state of consciousness. Many drugs cause hallucinations and cause euphoria. Legal drugs, notably Alcohol also alter consciousness as do many prescription drugs. These drugs act on the brain and show that the brain is critical in determining consciousness.