From this page of the Valheim guide, you will learn how to acquire Flax, a useful crafting resource.
Flax is one of the plants you can find while exploring the vast world of Valheim. The harvested Flax is processed on a Spinning wheel to make Linen thread, which can later be used to make armor parts.
Flax can be obtained from Fuling villages which can be found in the Plains biome. Flax can be picked up or cut down with a weapon. It can also be used to plant and grow your own crops, but only on the Plains.