The question is quite broad, but I'll attempt to give an overview in regards to the religious practices and stories we see commonly represented in pop culture.

Let's start with what we know about Norse mythology.

Most of what we know about the Norse religion was recorded long after the Christianization of the Scandinavian peoples. The 13th century Prose Edda (Snorra Edda), is a collection of stories presumably passed down through oral tradition in Iceland. We've gained a lot of knowledge through this source, but because of the nature of its creation, we can't say it's a wholly accurate portrayal of early Norse religion.

This text was written long after the religion died out in practice, so we have to be careful about taking it at face value. We have no way of knowing how the stories changed from the time of their creation to the time they were written down. Further, there were various groups living in Scandinavia not one amorphous group of "vikings" as is often portrayed in TV and in movies. They didn't necessarily have a homogenous culture or standardized religion. We also can't discount the influence that Christianity might have had on Snorri, or on the evolution of the retellings-- the Prose Edda overtly opens with a Christian story and references the flood from the Bible. We get further information from the sagas, but these were also recorded long after their creation. Neither are particularly concerned with the historic recording of religious practice, but are focused on the stories themselves (although incidentally religious practice does come up such as in the saga Heimskringla). This is why we know about Odin, Thor, etc, but don't have as much detail on how they were worshipped as we might like.

There are some practices we are fairly sure of. I'll look at three we see often in pop culture since this is where your question stems from.

Ship cremations:

We see a lot of cremation in ships in pop culture. While there was cremation (on pyres), what we don't see a lot in media is burials. From excavations like Valsgärde and Vendel, we know that important and/or wealthy members of society were buried with elaborate grave goods including weapons, jewellery, dogs, and horses. Sometimes they were buried in (or with) ships, and sometimes the ships were representative (such as the stone ships at Lindholm Høje). I also have yet to see mounds in pop culture, which is sad because they're quite impressive. Radar used on the mounds at Borre show buried ships and even entire halls. The Oseberg Ship was excavated from a mound in Norway with the bodies of two women and it's massive- quite impressive. So it really is a shame they don't show this in media as much, when we know this was a funerary practice in the region.

Animal sacrifice:

References to blót (sacrifice) are made in Heimskringla. Jól (Yule) was one such event, in which sacrifices were made to Odin. Heimskringla, however, has a very Christian bias, so take what you read from it with a grain of salt (such as the constant use of the term 'heathen' and 'idol'). Parts of a blót are described including:

-animals including horses being sacrificed and their blood being collected.

-smearing or possibly sprinkling "idols," other sacred objects, and worshippers with the blood.

-eating the remaining meat at a later feast/celebration in which Odin and Freyr were honoured.

References to blót are also made in Hyndluljóð, and Hrafnkels saga Freysgoða, albeit with a lot less detail*.*

Human Sacrifice

Blótkelda (human sacrifice) was also practiced. The medieval chronicler Adam of Bremen makes reference to human sacrifice at Uppsala in his Gesta Hammaburgensis Ecclesiae Pontificum, where he states that nine males were hung in sacrifice. He has a heavy Christian bias, keep in mind. Gautrek's Saga features an episode where Odin orders Starkaðr to sacrifice his friend, King Víkar, by hanging. Archaeological evidence also supports human sacrifice. In Lejre, the bodies of two men were excavated from a grave- one was decapitated and bound at the hands and feet. From a grave in Gerdrup, a woman was excavated alongside a bound man with a broken neck.

I'm sure someone else can expand further, but I hope that gives you an idea of where some things we commonly associate with the Norse religion are sourced from.

Sources:

Abram, Christopher. Myths of the Pagan North: the Gods of the Norsemen. Continuum, 2011.

Andrén, Anders (2011). "Old Norse and Germanic Religion". The Oxford Handbook of the Archaeology of Ritual and Religion. Oxford and New York: Oxford University Press.

Clunies Ross, Margaret (1994). Prolonged Echoes: Old Norse Myths in Medieval Northern Society: Volume 1: The Myths. Odense: Odense University Press.

Jesch, Judith. Women in the Viking Age. The Boydell Press, 2006.

“HYNDLULJOTH.” Translated by Bellows, Henry Adams. The Poetic Edda: Hyndluljoth, www.sacred-texts.com/neu/poe/poe15.htm.

Medievalists.net. “Why Icelandic Vikings Were Buried with Horses.” Medievalists.net, 7 Jan. 2019, www.medievalists.net/2019/01/why-icelandic-vikings-were-buried-with-horses/.

Pálsson Hermann, and Paul Geoffrey Edwards. Gautrek's Saga: and Other Medieval Tales. University of London P., 1970.

Sturluson, Snorri (1964). Heimskringla. Translated by Hollander, Lee M. (illustrated, reprint ed.). University of Texas Press.

Turville-Petre, E. O. G. (1975) [1964]. Myth and Religion of the North: The Religion of Ancient Scandinavia. Westport: Greenwood Press.