The language spoken by the ancient Vikings (and, by extension, their gods) was Old Norse–of of the Germanic Language Family Tree. They also had a writing system, known as runes. Runes are surprisingly easy to interchange with our modern alphabet as there are typically about 24-26 characters in the runic futhark.
A futhark is an alphabet in old norse. Our word alphabet comes from the first two letters in Greek: alpha, beta. The first letters in the Norse runes are fehu, uraz, thurisaz, ansuz, raido and kenaz, which together spell out futhark. With me so far?
Nordic runes were typically carved into wood or stone. Therefore the characters all feature straight, angular lines rather than the soft curves of the alphabet. The norsemen were pretty lax about things such as grammer and handwriting–runes can be flipped upsidedown or even mirrored for no apparent reason. There are multiple systems of runes varying by century and geographic region. There are very few surviving examples of runic writing, and this has led to the myth that they were used only in magic ceremonies, and only wizards knew how to use them.
The examples we do have of runes debunk this. There are lots of examples of runic graffiti in churches and on stones near meeting places, and it would seem that a pretty substantial percentage of vikings knew at least how to carve their name in runes. There are runestones found in the far reaches of viking exploration that attest to warriors who died, great feats accomplished, or simply “I was here” markers.
It is very hard to find an academic sourse to study runes. Most books on the subject want to also teach divination along with them. Runes are associated with divination for multiple reasons. Probably the main one is that the names of the individual runes (fehu, uraz, etc) are more than just meaningless pronouns. Fehu is the Nordic word for wealth, uraz means cattle, etc. It’s as if, when we learned the alphabet, we called the letters: “Apple, Ball, Cat, dragon.” Thus, when you cast the runes, you can interpret the letters according to the meaning of the word the character is named after instead of trying to translate meaningless gibberish.
There’s also the story about Odin piercing himself with his spear and hanging upside down on the branches of Yggdrasil for nine days and nine nights, at the end of which time he learned the magic of the runes and became even more wise and powerful than before. However, I would argue that being able to read and write in a tremendously important power right there and that runes don’t necessarily have to have any magical connotations in order to make a person wise!
For a good introduction to runes check out “Runes” by R.I. Page. It’s a fairly short book and covers both the linguistics and archaeology of rune-lore.