How are the Radleys different from the other people in Maycomb in To Kill a Mockingbird?

The Radleys are characters in Harper Lee's novel To Kill a Mockingbird. This novel takes place in the small town of Maycomb, Alabama.
In the town of Maycomb, most people are social with one another. The townsfolk often interact at gatherings or at church. It is common for the people of the town to sit on their porches and visit with neighbors as they pass by. This is something that happens frequently to the Finch children, Scout and Jem, as they walk to and from school.
The Radley family is different because they are reclusive people. Arthur and Nathan Radley do not often leave their home. Because Arthur "Boo" Radley is such a mystery, people have started to believe that he is a monster. Children in Maycomb, especially Scout and Jem, try to play a game to get Boo to leave his house. In reality, the Radley family is not a family of villains. They are people who want to keep to themselves and not cause any harm to society.

The Radleys differ from the rest of the community of Maycomb in several ways. Unlike the majority of the families in the small town, the Radleys are reclusive and do not participate in social events. They prefer to stay inside their home and do not socialize with their neighbors. They are also devoutly religious, and Miss Maudie tells Scout that Mr. Radley considered women to be a sin by nature. The Radleys also occupy a rather foreboding home that sticks out like an eyesore in the town. While most of the citizens of Maycomb are viewed as friendly and magnanimous, the Radleys have a reputation for being cold and mean. Even Calpurnia mentions that Mr. Radley was the meanest person she'd ever met after he finally passed away. Also, Mr. Radley's occupation is unknown and he is said to have "bought cotton," which means he does nothing for a living. Various rumors surround the Radleys, and they are a rather mysterious family. In the small, friendly town of Maycomb, Alabama, the Radleys are considered a unique family. 

Maycomb is overall a friendly town.  People enjoy visiting their neighbors, sitting on their porches in the evening, and going to church on Sundays.  The Radley family is different.  They do not do any of these things anymore.  Atticus tells Scout that they used to be different, a long time ago.  Over time, the Radley family becomes more and more reclusive:

[The Radley family] kept to themselves, a predilection unforgivable in Maycomb.  They did not go to church, Maycomb's principal recreation, but worshiped at home; Mrs. Radley seldom if ever crossed the street for a mid-morning coffee break with her neighbors, and certainly never joined a missionary circle (To Kill a Mockingbird, Chapter 1).

Members of the Radley family are rarely seen leaving their house.  They are seldom seen around town.  This is one of the reasons why bizarre rumors are able to circulate about Boo Radley.  No one in town sees Boo out and about.  They imagine what has happened to him.  The make up stories to explain his reclusiveness.
Sundays in Maycomb are an especially social time.  After church, people visit and socialize.  In the midst of this, "the shutters and doors of the Radley house [are] closed on Sundays, another thing alien to Maycomb's ways: closed doors meant illness and cold weather only.... [and] to climb the Radley front steps and call, 'He-y,' of a Sunday afternoon [is] something their neighbors never did."