The richest and purest source for the ideas and attitude to life of the early Teutonic people is the literature of Iceland during the twelfth and thirteenth centuries. When Icelanders began to write sagas about the events of bygone days, it was Christian monks who led the way with stories of the missionary kings of Norway, Olaf Tryggvason and "Saint Olaf". Snorri Sturluson was repelled by the pious remarks and unctuous style, and interpretation of the events themselves. His sagas are both more realistic and more entertaining.
The Upsala Codex, a parchment document from about 1330, is one of the most important manuscripts of the Prose Edda, or "Younger Edda", which was written by Snorri Sturluson around 1220 CE. It has four sections.
1. The Prologue, which consists of anthropological observations, which justify Snorri's retelling of the mythological tales. Snorri has used an orthodox Christian stance, identifying the pagan gods as ancient heroes deified by their ignorant followers. He explains the mythology as a the remnants of the history of a royal dynasty in Asia. (This may not be totally off the mark, given the evidence of runic alphabets found in Hungary and Turkey.)
2. Gylfaginning, "The Deluding of Gylfi": It consists of a story in which King Gylfi asks three kings, "High One", "Just-as-high", and "Third" about Norse mythology. Snorri was thus able to tell the myriad myths in a witty style, without speculation of their veracity.
3. Skáldskaparmál, "Poetic Diction", gives various kennings and elliptical references to the stories behind them. The poets of Sturluson's era were Christian, but were expected to still be able to write of the pagan mythology of two hundred years earlier. Snorri again uses the vehicle of a visitor to the Aesir, who is told stories. This section is the primary purpose of the Prose Edda, a discussion of the language and imagery of poetry, and how its metaphors can be understood in terms of Norse mythology.
4. Háttatal is the final part, a poem composed by Snorri about King Hakon and and Duke Skuli. The 102 stanzas are accompanied by a commentary in prose on the variations of meter and style exemplified by each verse. (I have yet to find an online version of this section of the Edda.)
The Northvegr (formally Midhnott Sol) site carries the Rasmus B. Anderson translation and the Arthur Gilchrist Brodeur translation of the Prose Edda. It is also available on the SacredTexts.com website. Woden's Harrow uses the Jean Young translation.
Lexicon of Kennings contains explanations of the obscure poetic references, by Eysteinn Björnsson and William P. Reaves.