To log out of Outlook, select your picture on the toolbar, and then select Sign out.
Important: Let's say you're sharing a computer with other people, and some of them also have Outlook.com accounts. To ensure your email doesn't automatically appear when they type "outlook.com" in the URL, always sign out of your account using this method. Also, turn off automatic sign in (see below).
How to turn off automatic sign in
When you log out of Outlook, uncheck Keep me signed in. If you accidentally forget to sign out of Outlook, when another person uses your computer and types "outlook.com" in the URL, they won't automatically get into your account.