How do you spell sounds or a moan?

Generally sounds are spelled phonetically. A moan could be "mmmmm" or "errrrggggh" (that's more of a groan). Some sounds develop a common spelling, but this can differ depending on the language used. For instance, in English, a cat says "meow," but in Japanese, it says "nyan" or "nya." You can see that the Words are derived from the actual sound when you look at the French -- "miaou" and Spanish -- "meow."