What is alliteration? Simply, it's a string of similar sounds at the start of several words in a sentence.
Why use alliteration? Mostly, it makes reading more musical and flowing, which is fun for friends to follow!
When I'm writing or editing (fixing and improving something I've written), and I'm looking for more interesting or unusual words to use, I will often choose words to create alliteration.
For example, instead of writing: " pretty, nosy cat" you could write, "cute, curious cat."
Instead of writing: "my friend mixed tomato sauce" you could write, "my sister stirred spaghetti sauce." If you go overboard with the alliteration, you'll end up with tongue twisters, which are really hard to read out loud without making mistakes.
Here are a couple of examples:
"If Stu chews shoes, should Stu choose the shoes he chews?" and "Santa's short suit shrunk."
You can read more tongue twisters here: http://www.funenglishgames.com/funstuff/tonguetwisters.html
While you're at it, check out a book called The Spaghetti Slurping Sewer Serpent. It was written by a friend of mine, Laura Ripes, and it's filled with tons of "S" alliteration.