What do you learnabout Bob and Mayella Ewell from their first brief appearance? (Why do Cal and the Reverend Sykes stop talking when they enter?)

I take it you are referring to the trial. Right away we can infer that Bob and Mayella are uneducated. Bob tries his best to get what attention he can by making ignorant remarks on the stand. The attention Bob is getting is more than any time in his life and he soaks it in. Mayella is scared. She is trying her best to lie but feels intimidated by everyone in the court room including her father.