One particular of the hidden rules of conduct between black and whites in Maycomb is exemplified in the scene in which Calpurnia brings the children to her church. For, even though the Finches have gone beyond what Aunt Alexandra believes is decorous in their affection for Calpurnia, unspoken rules are that she should not think that she is actually a member of the family. But, as she dresses the children for church, saying to Scout and Jem when they object,
"I don't want anybody sayin' I don't look afer my children."
The other members of Calpurnia's church are clearly aware of the hidden boundaries of racial conduct having been violated when they see the Finch maid enter with the children:
"What you up to, Miss Cal?" said a voice behind [them]...."I wants to know why you bringin' white chillun to a n-- church."
"They's my comp'ny," said Calpurnia.
"Yeah, an' I reckon you's comp'ny at the Finch house durin' the week."
A murmur ran through the crowd.
So, while it is acceptable for Calpurnia to take the children to town with her when she shops, she has overstepped boundaries by bringing them to a church that is designated exclusively for blacks.
As far as the black people of Maycomb go, the rules are pretty clear. Black people need to defer to white people in pretty much everything they do. They must not act in ways that imply that they think they are equal to the whites. You can see this in how the blacks in the community thank Atticus Finch by putting food on his back porch. They know that black people must not come to a white person's front door.
For whites, it's more complicated. They ought to be paternalistic towards their black servants. They are supposed to take care of the black people. This is a rule that the ladies of the Missionary Circle have broken when they complain about their servants after the trial. At the same time, they are supposed to act in ways that maintain white supremacy. An example of this can be seen as Aunt Alexandra wants Atticus to get rid of Calpurnia because she is not a good enough influence on Scout.