Complex sentence: Aunt Gerda tells it's time for Clara to sleep, and so Uncle Drosselmeyer says good night to Clara and exits, saying "Tick, tock, tee..." over and over.
Split into simpler sentences: Aunt Gerda tells it's time for Clara to sleep. So, Uncle Drosselmeyer says good night to Clara and exits, saying "Tick, tock, tee..." over and over.