In Chapter 1, Scout provides a brief background of her family's history. Then she gives brief descriptions of certain people in Maycomb. As Scout and Jem give Dill all the details about the Radleys, Dill becomes more and more curious about Boo. Chapter 1 focuses on Scout's overview, but most particularly on meeting Dill and the mystery of Boo Radley.
Scout recalls the time when Boo allegedly stabbed his father in the leg with a pair of scissors. Since his father, Mr. Radley, didn't want the disgrace of having a family member sent to the asylum, Boo was subsequently locked in the courthouse basement. Boo was thirty-three at this time. Boo went back home and was never seen in public. Jem figured that Mr. Radley kept Boo chained to the bed:
Nobody knew what form of intimidation Mr. Radley employed to keep Boo out of sight, but Jem figured that Mr. Radley kept him chained to the bed most of the time. Atticus said no, it wasn’t that sort of thing, that there were other ways of making people into ghosts.
Atticus remarks that there are other ways of "making people into ghosts." Atticus means that there are other ways of keeping people out of sight, out of the public eye, essentially imprisoned. Atticus is suggesting that Mr. Radley uses mental abuse and manipulation to keep Boo in the house. Since Boo is never seen at all, it is like he is a ghost.