Think of someone who just can't stop talking, even if they aren't saying anything particularly interesting or important.
Here are some synonyms for "garrulous":
* Talkative
* Chatty
* Loquacious
* Rambling
* Prolix
* Voluble
Here's an example of how you might use "garrulous" in a sentence:
"The garrulous old man at the bus stop told me all about his grandchildren, his cat, and the weather, even though I just wanted to get to my destination."