On this page of the Valheim guide, you will learn how to get Turnip Seeds and what you can use them for.
Turnip seeds are one of the seeds that can be found as you explore the world of Valheim. Turnip seeds can be planted using a cultivator – they grow into Turnips. Raw turnips are not edible, but you can use them to make a Turnip stew.
Turnip seeds can be found in the Swamps biome - they grow on thin stems and have distinctive yellow-green flowers. You can see them in the image above.