What just happened?

You signed out of your Office Live Small Business account. You could simply have closed the browser window, but that's not really prudent.

Whenever you sign in, the Windows Live ID authentication system stores some information in browser cookies so that you don't have to sign in repeatedly. Closing the browser window doesn't get rid of the cookies. So, anyone who uses your computer after you, has full access to all your accounts attached to your Windows Live ID. When you sign out explicitly, as you just did, the cookies are deleted and others can't access your account accidentally.

Another benefit of logging off, and thereby deleting the cookies, is that your computer doesn't "remember" anything from your previous session.