From Georgetown University Commons Knowledge Base
Select the "edit" next to public
Before publishing your new post you will have the option to change the "Visibility" of the post. On the right of the screen, the "Publish" box will allow you to "edit" the visibility of the post.
Select Private and Press Ok
When you select "edit," an expanded menu will give you the option to either make your post public, password protected, or private. By selecting "private" the author of the post (the author) and the administrator of the blog will be the only users that can view the post.