The elder Futhark is the most ancient Germanic runic alphabet. The word futhark is formed after the first six runes in it, the same way as the Greek word alphabet is formed after the first two Greek letters, Alpha and Beta. See below which signs represented which sounds:
The order of the runes has nothing to do with the ABC and clearly developed independently. As for the runes themselves, there is no agreement on their origin: some researchers are inclined to think that runes were greatly influenced by the Roman alphabet, others point to Etruscan writing from Northern Italy. As it seems, the oldest datable runic inscription is on the comb from Vimose (ca 160 AD). The elder Futhark remained in use until the ninth century, when it was superseded by other runic systems due to the phonological changes in Germanic languages, which made it less suited to render the current speech sounds.