If you want to use fuling totems to summon the final boss in Valheim, you will need to start by looking inside fuling villages.
You can farm fuling totems by raiding fuling villages, as they spawn pretty often inside most villages you can encounter in the plains biome - see the image above for an idea of what to look for. You can also farm fuling totems from fuling berserkers as they will have a small 10 percent chance to drop the totem upon death.
However, you should be careful before venturing in as fulings are extremely dangerous despite their small size and can one-shot you even in wolf armor.
Related: How to farm Bloodbags in Valheim
So we recommend bringing only the best armor and weapons you have in your arsenal to defend yourself - this would more or less be iron armor that is fully upgraded.
That said, once you are adequately prepared, start by looking for a plains biome, and when you have found a plains biome, you are going to want to look for large structures like the one below.
Along with this, if you plan on farming the berserkers, they will also have a tendency to spawn around the villages. You will also need to get a total of five of these totems if you plan on using them to summon the last boss in the game.