In this quote, Scout is expressing how Aunt Alexandra upheld all of the old class prejudices, unwritten laws of behavior, proper social attitudes, and elaborate historical implications of Maycomb. She knew who all of the "right folks" were, which families to stay away from, what beliefs to have about each and every individual in the town, based on generations of stereotyping and gossip, and what one needed to do to better "fit in" in Maycomb. She knew that if you were to be in the social loop and be included and looked well upon, you had to join the missionary circle, go to church every week, be social, and pass on ages-old tidbits, beliefs and attitudes about everyone in the town, along with their dogs and cats.
Jem and Scout, under the constant tutelage of Atticus, have been raised to question all of the old stereotypes, and to judge people on the content of their characters, not what family they come from. Even though they are aware of Maycomb's families and all of their quirks (look at how Scout fills in her teacher in chapter 2), they are more open-minded. They don't fit in super well either because they are guilty-by-association with Atticus, who is going against the grain in defending Tom, a black man. So, they are different; they defend their differences, and set themselves apart with them. On the other hand, Alexandra tries to fit in, to not stand out, and endorses some of the beliefs and attitudes that Atticus works so hard to challenge. I hope those thoughts help; good luck!