While Onomatopoeia is a mouthful, the concept is quite easy. The actual word derives from Greek, meaning "name" and "I make". In layman's terms, it's a word that resembles the source of sound it describes.
It makes sense that onomatopoetic words differ from language to language. I remember when teaching the English words of animals to young children in Korea, I showed them a picture of a cat, and then imitated its sound - Meow. Then they taught me that the cat sound in Korean was Yaong!
But alas, this is an English language blog, so I'll stick to only English words.
Here is a list of words that sound like they actually sound:
Bang Crack Squish Beep
Boom Snap Gurgle Sizzle
Pop Rustle Roar Buzz
Splash Drip Purr Ring
Wham Poof Slurp Growl
Can you think of any others?