From this page of the guide to Valheim, you will learn how to get Guck, a resource useful for crafting.
Guck is one of the resources that can be found while exploring the vast world of Valheim. It is used to create torches, banners and the Draugr Fang bow.
Guck is obtained by smashing the Gucksacks that can be found in the Swamp biome. You'll have to use a pickaxe or an axe to get your hands on this resource - bows, spears and daggers don't do any damage to the Gucksacks.
Gucksacks may grow in higher parts of trees, which makes them difficult to access. If this is the case, place a Workbench nearby and build some stairs by the tree, or surround the tree trunk with floor panels so that you can jump between them freely.