Your sentence is: "Goose down makes an excellent filling for pillows and down jackets."
This sentence is grammatically correct! It means that goose down is very good for stuffing pillows and warm jackets because it is soft and warm.
If you want, you can learn about what goose down is: it's the soft, fluffy feathers from geese that keep them warm. People use it to fill cozy things like pillows and jackets.