Meaning: severe or strict:
* The stern teacher demanded complete silence from her students.
* The captain gave a stern warning about the dangers of the storm.
* His stern expression made it clear he wasn't happy.
Meaning: relating to the back part of a ship or boat:
* The ship's stern was decorated with intricate carvings.
* The crew gathered at the stern to watch the sunset.
* The stern of the boat was battered by the waves.
Meaning: relating to the back part of a vehicle:
* The car's stern was dented in the accident.
* The bus had a large compartment in the stern for luggage.
Let me know if you would like more examples!