The first occurs when Scout demonstrates that she is a very accomplished reader on the first day of school, which annoys Miss Caroline. Miss Caroline tells Scout that she must tell her father to stop teaching her how to read.
The second altercation happens when Miss Caroline catches Scout writing a letter to Dill, and again orders Scout to tell Atticus that he must stop teaching her how to write. According to Miss Caroline, Scout won't even learn to write (cursive) until the third grade - they only print in the first grade. Scout knows how to write cursive because Calpurnia taught her at home.
The third occurs when Scout tries to explain Walter Cunningham's situation to Miss Caroline, who simply does not know the people of Maycomb County yet. Miss Caroline tried to give Walter a quarter to buy lunch, but he refused to accept charity. When Scout tried to explain this to Miss Caroline, she was slapped on the hand with a ruler and made to stand in the corner.
Be sure to do a careful re-read of Chapter 2 if you missed any of these when you read the book. Also check the eNotes link below. Good luck!