Heathen practice is reconstructed rather than inherited, and the honest question about any reconstruction is what it is reconstructing from. For the pre-Christian religion of the Germanic peoples the answer is uncomfortable and is best stated plainly.
Written by the other side
The Poetic Edda and the Prose Edda are the fullest sources for Norse myth. The Prose Edda was compiled by Snorri Sturluson in thirteenth-century Iceland, two centuries after the conversion, as a handbook for poets who needed to understand the old references. He was a Christian writing for Christians about a religion nobody around him practised. Tacitus, writing about the continental Germans, never went there. Adam of Bremen described the temple at Uppsala as an opponent and at second hand. Almost nothing survives that was written by a practitioner while the practice was living.
What the ground supplies
Archaeology gives what texts cannot: burial goods, hall sites, sacrificial deposits in bogs, amulets, and the runic inscriptions, which are short and mostly practical. This material is contemporary and it is mute about belief. It tells us that something was done and rarely what it meant.
The gap, and how it is handled
Between those two bodies of evidence sits everything a modern practitioner actually does: the form of a blot, the words of a toast, the calendar of holy days. Some groups reconstruct as tightly as the evidence allows and say where they have stopped. Others fill the gap frankly with modern invention and say so. The disagreement between those two approaches is one of the live arguments inside the movement, and it is a methodological argument, not a theological one.