Final answer:
The brain knows what's out there through sensory organs and the nervous system, which receive and process information from the external world.
Step-by-step explanation:
The brain, even though it is locked away in darkness inside the skull, is able to know what is happening in the external world due to the sensory organs and the nervous system.
The sensory organs, such as the eyes and ears, receive information from the environment and send signals to the brain.
The brain then processes these signals and interprets them as sight, sound, touch, taste, and smell. This enables us to perceive and understand the world around us.