In this section I will be talking about misconceptions about Norse Mythology that have been propagated by popular media and young adult literature like Marvel, Magnus Chase, or Loki's Wolves. This is not meant to discredit these works as they are great entertainment and I would recommend them to anyone but they do get things wrong as it apply to true mythology and I believe you have to know the correct information to learn Norse Mythology without getting confused.
I will also be listing out any mysteries from Norse Mythology that are likely explained by outside culture, like why things might have originated in the mythology without any direct mechanism.
This assumptions from this section are a combination of things I know have been incorrectly portrayed, things I though were correct till I researched further, an Interview with my friend about what he know of Norse Mythology based off only consuming the aforementioned media, and some research.
Loki is probably one of the most misrepresented characters in Norse Mythology. The largest misconception is that he is Thor's brother and Odin's son. Loki actually isn't related to any of the other gods, he is a giant born in Jotunheim and doesn't meet the gods until later. We don't actually know how Loki came to meet the Aesir or how their bond happened but we know that Loki and Odin have a blood pact together so they are referred to as blood brothers. The actual relationship between him and Thor is just a strong friend ship. Loki causes lots of mischief and trickery throughout the myths but he isn't a god and therefor can't be the god of them.
Another misconception is that Loki supports the Aesir at Ragnarök, but Loki is actually the cause of many of the problems at Ragnarök. This is mainly due to him fathering Jörmungandr the Midgard Serpent, Hel who is half woman half corpse and rules Helheim, and Fenrir The Wolf with the giantess Angrboda.
Aside from most of the Marvel movies being made up adventures the main misconceptions around Thor are of his appearance and his weapons. In current media Thor is often portraited as this handsome guy with flowing blond hair and a six pack. While the myths don't mention his abbs they do tell us that he was just ok looking, maybe even a bit ugly with his face being messed up from fights; he also had ginger hair, and wasn't all that smart.
Thor also didn't get Mjolnir from Odin. In one of the stories Loki cuts off all of Sif's (Thor's wife) hair and takes it from the roots so it can't grow back. Thor then threatens to beat Loki within an inch of his life every day till Sif's hair grows back so Loki has to come up with a plan. To appease Thor and the other gods Loki creates a competition between two sets of dwarven brothers. To convince the second pair to join Loki has to promise them his head if they beat the triplets that Loki's backing. Loki of then tries to cheat and causes most of the second pairs gifts to be slightly broken. The last of the second pair's gifts is Mjolnir which shorter than it was supposed to me making it a one handed hammer instead of two handed.
Odin in the myths if quite different from the Odin portrayed by Marvel. He is portrayed as a wise present king and stern father; but in actuality, Odin, while still wise, is shown as wanderer and shaman in Norse Mythology. In fact, in the story about the Mead of Poets he takes on the name of Wanderer when living among the Giants for an extended period of time. Marvel also implies that he lost his eye in a battle with the Frost Giants but in mythology he cuts out his own eye as a sacrifice to Mimir so he could drink from the Well of Knowledge. He is also portrayed as stuck up and hating of mortals but in mythology he consistently sacrifices for wisdom like with his eye or hanging from Yggdrasil and often wanders among humans and occasionally shared his wisdom.
As I mentioned on the home page Hel appears as a beautiful woman from one side and an ambulatory corpse from the other. In media she has been portrayed as fully human looking. She also chose to go to and rule over Helheim at Odin's offer; and finally her role in Ragnarök has been overstated, she is simply Loki's general for the armies of the dishonorable dead from Helheim.
There is no clear origin of the Vanir in either of the eddas. When they are first mentioned we are simply told that they are at war with the Aesir. In The Echo of Odin, Smith hypothesizes that the Vanir likely represent a waring belief group or cult.
When the Vikings ran into followers of Christianity, through trade not concurring, many people wanted to convert them. This interaction of culture led Henry Longfellow to write The Challenge of Thor where Thor challenged the "Galilean" to personal combat. Some young adult literature like Magnus Chase has presented this as part of myth when it isn't.
Due to the Vikings constantly waring with other cultures and peoples they often adopted the attributes of other gods into their own. Some of the most notable are the Roman Mythology (in Greek Mythology) characters of Hercules (Heracles) and Mercury (Hermes) in the characters of Thor and Odin. Thor and Hercules are compared largely due to their great strength and some say its because they both have a signature weapon. Odin and Mercury have many similarities, they are both figures that travelers will meet on the road where they will give wisdom, more loosely Mercury is also the messenger god and Odin's ravens are used to send messages.
While Norse Mythology doesn't have as large of an impact as Greek or Roman Mythology on modern culture but it is still present. Several festivities around Christmas time like the Yule Log can be traced back to Norse Yule Fests which come from Odin's epithet Jólnir meaning Yule-One. We also find the Norse Gods in our English days of the week, Tuesday from Tyr, Wednesday from Odin (sometimes translated as Woden), Thursday from Thor, and Friday from Frigg or Freya.