In the most mundane sense, runes are an alphabet much as our own alphabet and others such as the Greek and Cyrillic alphabets. Each rune represents a sound and was/is used to write words with.
But that is in the most MUNDANE of senses.
Runes were used long before the concept of writing was around. Each rune is an archetype of a force. People had concepts for such things as Fire, Honour, Birth, et.al. and each of these concepts were given names to make them easier for us to comprehend. In this way, runes are very similar to the Hebrew alphabet. Each 'letter' not only has a sound and a name, but is a complete word with all associated concepts.
This similarity with Hebrew extends even farther. Each hebrew word is made of several Hebrew letters, therefore each Hebrew word is made of several Hebrew words. The initial letters of several words in a sentence, or of the first letters of each sentence or paragraph may be gathered to form a new word that is used to help explain and expand upon what is already written. The same can be done with runes.
Runes lend themselves readily to numerology. The Runic alphabet is properly shown as three rows of eight letters. Therefore each letter can be identified by row:column number. Additionally, each rune has it's sequential number identified by it's placement in the alphabet. Much like us numbering A as 1, B as 2, ... , and Z as 26.
Each rune can be placed in position on a tree pattern much like the traditional Qabbalah. They may represent the different worlds or paths of the tree and can be expanded and expounded upon as much as the Qabbalah itself is. In fact, Runic Qabbalah is quite intriguing and does contain a life of study (as do all other facets of Runework).
Runes can be used for fortunetelling. They can be drawn and placed and read much like tarot cards. The can be cast or strewn and the relationship of groupings, distance and angles and patterns formed will tell the caster what he wishes to know.
Runes are also entities in and of themselves. Much like the angels, princes, demons, sylphs, undines and watchtowers of the ceremonial magician. Each rune can be invoked or evoked and the power harnessed to work ones' will to enlighten the intellect. They are a fantastic meditation tool and will always increase ones' knowledge.
Much as the primal elements of Earth, Water, Air, Fire and Spirit, each rune also has it's part in the manifestation of all things manifested. Chaos, grass, people, sunlight, honour, dragons, hopes, and sex are all replete with runes and could not ever exist without the runic force that creates, shapes, releases, destroys and changes them.
I have equated runes to many other branches of esoteric, occult, phsycological and intellectual pursuits. This is in the hopes that if you are already familiar or interested in one of these, you will realize that runes are already familiar to you or that you are already interested in them and don't yet realize it.
May you approach the Well of Wyrd and may your sip there only increase your thirst.