On page one, Junior says, “"I was born with water on the brain. Okay, so that's not exactly true. I was actually born with too much cerebral spinal fluid inside my skull. But cerebral spinal fluid is just the doctors' fancy way of saying brain grease. And brain grease works inside the lobes like car grease works inside an engine. It keeps things running smooth and fast. But weirdo me, I was born with too much grease inside my skull, and it got all thick and muddy and disgusting, and it only mucked up the works. My thinking and breathing and living engine slowed down and flooded." Why does Alexie start with this information? What is he telling the reader?
The tone of the this information also begins to establish Junior has a sharp witted and funny young man who doesn't take himself or his situation too seriously. By using this casual language you "hear" the voice of a young first person narrator who is going to see the world from that perspective and will tell serious events in sometimes not-so-serious language and tone. You are getting to know him on the first page.
Junior means he was born with a condition known as hydro-encephalitis in which cerebrospinal fluid fills the cavities of the brain and often causes great damage, including mental defects. He means, obviously, that his thinking is not clear, he does not function mentally as well as an otherwise normal person would as a result of this birth defect. He compares his mental processes to those of an automobile engine which is has been flooded---it doesn't want to start or run well.