For instance, let's take the Younger Futhark alphabet. How do you build a word? By just getting the first letter or phoneme of the name of each rune? Or do they have a contextual meaning?
A runic alphabet works like other alphabets: one rune corresponds to one or more specific sounds. Runes only really have one significant difference: they are designed to be carved in wood, which means that they usually have vertical or slanted straight lines, but no or very few horisontal and curved lines.
However, as the Younger Futhark was specifically mentioned, I will point to a few special features when this is used for Old Norse:
As for other meanings, we have names for the runes coming from medieval or foreign sources and some knowledge of how the sound values have changed, which has allowed us to recreate the original names and meanings. Such meanings are very usual in longer texts, but it seems like they could have been used as magical inscriptions. Their main use seems to have been as a memory aid, so that the "i" rune was named "is", 'ice'. However, one shorthand was rather common, and even found its way into texts written with the Latin alphabet: the "m" rune, named for 'men' was used as a shorthand for "man" in medieval manuscripts.
I'm basing most of the above on Lars Magnar Enoksen's Runor.