Suppose you have a draft article ready for publication but you need a review before publishing the article. To notify other users in your account of an article, go to the specific page as if you were editing it. In the sidebar on the left, you'll find the green 'Publish options' button.
There, you'll find the 'Notifications' option:
Click on the 'Notify Users' button. This opens a pop-up with a list of users, a subject field and a message field. Click on the checkbox to select one or more users and fill out the 'Subject' and 'Message' fields.
When you're done, hit 'Send'.