This will open up a field for you to post a status message. On the left side, you'll find check boxes for "Facebook" and "Twitter." Decide where you want to publish the post by checking them off. This is an especially helpful feature, as you may not want to burden a lot of your Facebook friends with your daily work-related tweets.

Some other cool things the Tweet editor does: it will automatically shorten URLs and add them to the body of your tweets before you send them. You can also upload pictures to TwitPic, a service that hosts pictures that are shared (via a link) over Twitter.