How do you spell the Japanese alphabet?

You can't. Japanese doesn't have letters like English and similar languages do. It has a complex set of characters (the most commonly known of which is "kanji"). Each character makes a sound. For example, 火 makes the sound "ka". These sounds, or characters, then build a word. So for example (a wild example, but an off-hand one), 火術 would spell out "kajutsu", or "fire technique" (as drawn from an anime I'm into right now).

There are hundreds of characters just like this, which makes Japanese a rather difficult language to master!