1. Currency:
* The price of the sushi was 1,000 yen.
* She exchanged her dollars for Japanese yen.
2. Desire/Urge:
* I had a sudden yen for a cup of coffee.
* He had a yen to travel the world.
* The kids had a yen to play outside.
3. (Archaic) A coin:
* This old coin is worth a yen or two. (Less common usage)
Remember that "yen" can be singular or plural, depending on the context.