Onomatopoeia refers to words which make the sound they suggest, e.g. zip, crack, crash, buzz. Onomatopoeia is hard to say and even harder to spell, however it's not as scary as it looks!
Onomatopoeia can be used in an unsubtle way, as you might remember from childhood books and nursery rhymes. The writing of animal sounds is an example of onomatopoeia. Sounds to replicate those of nature or of terrible accidents are familiar, too, and you might have seen onomatopoeia in graphic novels as visual sound effects.
Poets and other writers use onomatopoeia to make you "hear" particular sounds when reading, as when they write of "reeds whispering", "branches creaking" or "water gurgling". It's good to experiment with onomatopoeia in order to make your writing more interesting, but try to use it sparingly and inventively, since many of these phrases have become cliched over time.There are two quizzes on the subject, so to sharpen your onomatopoeic skills, give them both a go!