Complex sentence: The next day, on May 21, Kinkel drove his mother's car to the school, armed with the rifle and two pistols, and, wearing a long trench coat, he entered the cafeteria and began shooting at students with the rifle.
Split into simpler sentences: The next day, on May 21 Kinkel drove his mother's car to the school. Wearing a long trenchcoat and armed with the rifle and two pistols, he entered the cafeteria and began shooting at students with the rifle.