Twit-what?

Can someone PLEASE explain Twitter to me? I just don't get it.
I've been hanging in the forums of Artfire and I'm REALLY excited about my new shop there. Lots of people are talking about Twitter to promote your business, so I joined.
What's the point? Really, I get enough rescue email in a day to choke a crow, so I'm not sure I want my inbox flooded with "I'm having a Starbucks".
Please enlighten me? I'm all about this social networking thing, especially since it can get pretty boring looking at a sewing machine and mountains of fleece all day and especially on days when I'm not feeling all that crafty.
I get Facebook, but I'm just not sure I am understanding the drift of Twitter.
God, I'm getting old.....