Complex sentence: The Æsir used this gold and stuffed Ótr's body with gold and covered its skin in gold and covered the last exposed place (a whisker) with the ring of Andvari.
Split into simpler sentences: The Æsir used this gold to stuff Ótr's body with, and covered his skin in gold. They then covered the last exposed place (a whisker) with the ring of Andvari.