Inthe novel, "To Kill A Mockingbird," what tense situation occurs at the county jail? How does Scout help her father in this scene?

The scene at the county jail is tense because Tom  Robinson, who has been accused of raping Mayella Ewell, is being held there. Atticus anticipates trouble with some townspeople and decides to sit on the porch outside the jailhouse.

As he expected, a mob of white men arrives to take the law into its own hands. They clearly intend to take Tom Robinson, by force if necessary, and administer their own justice. Against their father's orders, however, Jem and Scout go to the jailhouse where they encounter the angry mob. Scout, too young to understand what is happening, recognizes Mr. Cunningham, the father of one of her classmates, and strikes up a conversation with him.

This small act humanizes Mr. Cunningham; he becomes ashamed of his behavior and convinces the other men to leave peacefully.