Short answers, pulled from the story.
The National Library of Sweden in Stockholm holds a single manuscript known as Codex Holm B 64. This document dates to the 13th century and contains the text of Gutasaga alongside the Gutalag legal code.
A man named Þieluar discovered an island that remained submerged under water during daylight hours. He broke this spell by lighting a fire upon the shore to free the land.
Three brothers divided Gotland into distinct sections where Graipr held the northern third, Gute claimed the middle section, and Gunnfjaun took control of the southern third. This legal division persisted until the year 1747 when it finally ended.
These emigrants journeyed to Þorsburg but were chased away from that location before moving on to Faroy. A group settled on an island called Dagaiþi close to Estonia and traveled up-river through Russia along the waterway known as the Dyna before arriving in Greece.
This event occurred before the end of the 9th century when Wulfstan of Hedeby reported the island was subject to Swedish rule. The text asserts duties and obligations for both the Swedish king and bishop regarding Gotland.
Names from the saga appear on modern places like Tjelvar's Grave stone ship located in Boge and a cairn in Garde known as Digerrojr. In 2011 the Swedish Astronomical Society hosted a competition to name a newly discovered Apollo asteroid found in Visby which received the designation 137052 Tjelvar.