Short answers, pulled from the story.
The Völsunga saga is a late thirteenth-century prose rendition written in Old Norse. The physical manuscript that preserves this text dates to approximately 1400 and resides in the Royal Library of Denmark as Ny kgl. Saml. 1824 b 4to.
Sigmund survives a she-wolf attack and burns Siggeir alive while his son Sigurd slays the dragon Fáfnir. Guðrún avenges her brothers by killing Atli and setting their hall on fire after he orders Högni's heart cut out.
Odin appears as a hooded one-eyed man who thrusts a sword into the tree Barnstokkr for Sigmund to pull free. He later breaks Sigmund's sword during battle and guides his son Sigi out of the underworld at the beginning of the story.
Loki takes gold from the dwarf Andvari to fill Ótr's skin with gold after King Hreiðmarr demands payment for his death. This treasure includes the cursed ring called Andvaranaut which brings death to whoever owns it.
Richard Wagner composed Der Ring des Nibelungen based on this saga while Ernest Reyer created an opera named Sigurd that draws directly from the text. J.R.R. Tolkien derived The Legend of Sigurd and Gudrún from the Völsung poems found in the Elder Edda rather than the prose saga itself.