While you are writing an article on a live site, you may not want people to be able to see it until you are ready, but you want to see it on the web site for your review.

You can set the Access to Registered, then it won't be visible to the public.  If it is part of a Category Blog or a Category list, it won't show up except for registered users. If it is not part of a Category Blog or list, and you plan to make a Menu Item -> Single Article with it, you should go ahead and do so, but set that Menu Item to have a Registered Access Level as well.

If you have a number of Registered users that you don't want seeing the article either, create a new User Group and assign it to a New Access level under Registered.  Assign yourself to the new User Group, then set the Access Level for the Article to that new Access Level.  Since you are the only one in that User Group, then you will be the only one that can view the Article from the Front End.  If you want it available to someone else for review, then add them to that new User Group as well. 

You will need to log into the site on the Front End and navigate to the article for review.

If your site does not have a login form on the front end for security reasons or they don't want to have one for other reasons, there is a way to get to a login form for any Joomla site. Add one of the following to the end of the URL for your site in the address bar of the browser.

/index.php?option=com_users&view=login

or 

/component/users/?view=login