Hah, this is great. Next time your luddite mother asks your in confusion what all this “twittering” is about, just send her over to this site. Jessica Hische lays it out nice and clear.
Twitter is awesome, but while it seems like a relatively simple service, it is quite nuanced. I hope this site helped you or someone you know get acquainted with twitter so that you can stop writing your tweets incorrectly, accidentally airing your dirty laundry to the internet at large. I am not an employee of twitter, just an avid (understatement) user of the service that wanted to lend a hand to twitter n00bs. This site is not a comprehensive guide as twitter is always adding new subtle features to make their service more useful and user-friendly, but this should demystify most of the basics. You can always visit support.twitter.com to find out more.