Just a few comments here.
Firstly there are a number of different runic alphabets. The most commonly used is the Elder Futhark which does consist of 24 characters. On the other hand the Younger or Anglo-Saxon Futhark has 31 characters. The Elder Futhark dates back to perhaps 1000 BCE; however, the most ancient runic inscription we have dates from only 200 AD. Both the Elder and the Younger Futhark were used for writing in Nordic Europe up into the Middle Ages. The Medieval Futhark was based on the Latinized alphabet. In addition, there are a number of regional runic systems. http://sunnyway.com/runes/runic_scripts.gif
Runes have been used since ancient times as a system of writing, as a means of divination, and in magic. Tacitus, a Roman historian, writes about the Germanic tribes using runes for divination. For divination and/or magical work runes were traditionally made from wood or metal...oak being a favored wood, particularly one that had been struck by lightening.
The legend of the origins of the runes, at least the Elder Futhark, is that Odin hung upside down upon Yggdrasil (the World Tree) impaled on his own spear for nine days and nine nights (probably reflecting the Nine Worlds that circle the World Tree). When the runes appeared before him he grasped them and drew them up...later sharing them with Freya.
Some good books on the subject of runes include:
" Taking Up the Runes " by Diana Paxson
"Futhark: A Handbook of Rune Magic" by Edred Thorsson
"The Way of the Runes" by Bernard King
"Practical Guide to The Runes" by Lisa Peschel
And some of my favorite websites on the subject:
http://sunnyway.com/runes/ Probably the best I've been able to find.