To Kill A Mockingbird reveals the effects of narrow-mindedness and intolerance in the extreme. As the narrator, Scout commences the story of the innocent Tom Robinson's trial and conviction for the rape of Mayella Ewell by tracing the Finch family history. It is significant that she notes how important social standing is in Maycomb County and how it is "a source of shame" that the Finch family cannot trace their family back any further than Simon Finch. Scout mentions that it has always been a family tradition for the Finch men to make their living from cotton (which was a major source of income in the southern states) but Atticus, Scout's father, studied law and his brother Jack studied medicine instead. This reinforces the fact that Atticus is not a typical Maycomb County resident; in the 1930s his sense of equality and fairness is unique and is Tom Robinson's only hope in a town where racial prejudice is the norm and hypocrisy goes unrecognized by most.
There is a reliance on tradition in Maycomb County and Scout discusses the predictable activities of most of the townspeople for whom there appears to be no motivation or desire to change. Therefore, in this "tired old town" those folks who do not conform are frowned upon and the Radley family has its own special reputation of housing the "malevolent phantom" (chapter 1) which results in unwanted and unmerited gossip about the Radley family, especially Boo. There is a false sense of community in Maycomb and anyone who does not participate in this conceited and insincere version of polite but bigoted society must expect and accept stinging and unfair criticism.
The Radley family members have always "kept to themselves." The only interaction that takes place is when Mr Radley regularly goes to town to buy what are presumed to be groceries. However, Scout cannot confirm or deny this and the only thing Scout knows is that Jem tells her that Mr Radley "bought cotton" which term Scout tells the reader is "a polite term for doing nothing." From an economic perspective, the southern states had relied on cotton historically and so this term infers that Mr Radley has no source of income from employment and lives on welfare.
If you think about the lifestyles of those who lived in the south during the time period in which the novel is set, it should be relatively easy to understand that someone who "bought cotton" did nothing for a living. Those who literally did buy cotton for a living (to sell, etc.) would probably have lived pretty easy lives in the eyes of those who did physical work, such as picking cotton. To those who were in the fields, it probably seemed that men who spent their days in offices, etc., really did nothing.
It simply means that he does nothing for a living. He might have money coming in from an inheritance or something like that. While he doesn't do anything for a living, this is quite different from some families in Maycomb, like the Ewells, who live off "the bounty of county," which would be well-fare.
scout means that mr. radley did nothing