Complex sentence: Milhouse talks back to Mrs. Krabappel, wanders away from the group and causes mischief with Bart, and tells Bart he does not care what anyone thinks of him anymore.
Split into simpler sentences: Milhouse talks back to Mrs. Krabappel and wanders away from the group. He causes mischief with Bart, and tells him that he does not care what anyone thinks of him anymore.