How to blog via url

How to blog via url: So, if your login account has more than one blog you will see a drop down list of all blogs available to your account. Also there is a Logout link. I wonder if the message body (this text) is preserved when I click Logout (so that I can login as a different account and publish it to a different blog) ... - YES! it does (although I logged in with the same account, but I did log out and the text I typed in was not lost). Good work, someone!

So, next question, how do I pre-select a blog via url?