It's called Casting Lots, which can be done with stones, bones, pieces of wood, or any material that you can write/paint a rune on (I have seashell runes as a gift from Mz.Kalamity that I use more for ritual as seashells are fragile and not good for casting lots).
Essentially what you do is pull a handful and toss them lightly onto a surface and interpet how they fall. There are various techniques for interpretation and it's really easy searching for them online, though when you understand each rune and how they affect one another in a reading (not terribly unlike Tarot in that each card affects another in a spread), you might begin to develop your own understanding of how to read the positions of each rune that has been cast.
These next sources touch a little bit on what the runes are in the context of medieval Scandinavian culture and religion, as well as explaining the source of our understanding of each rune; the Rune Poems. Your first step is to identify which set of runes you have.
You can also make use of the Galdrastafir, which are Icelandic sigils used in spellcraft (literally translated as "spell/incantation staves"). As the runes were used as a linguistic system in addition to magical and religious uses, they were always made with straight lines (and almost never horizontal as it was often hard to carve "against the grain"). Galdrastafir, on the other hand, were written with more specific and magical intent and thus people put more time into writing, carving, and painting them, which allowed for the curved lines you see with them.
I haven't been able to look this over in-depth, though at a glance it appears to be good information to start off with (though you will always want to validate your sources and cross reference them; this would be a starting point to expose yourself to Galdrastafir).
And finally for now, a video by Personified that explains what Galdr is and how to practice it.