WordPress allows you to control the visibility of your posts and Pages on an individual basis. By default, all posts and Pages you publish in WordPress are visible to everyone.
If you want to password protect specific blog posts, you can do that by modifying the Visibility settings within the Post Editor. You can password protect individual post so only a select group of people can read it.
Protected post is different from Private post. The Protected post is protected with a password you set. Any user that has the password can view a protected post but the Private post is only visible to blog Editors and Administrators.
How to Password Protect WordPress Post
To password protect a post, open the post for editing, click Edit next to Visibility: Public in the publish module, select Password protected, enter a password, click OK, and click Update Post to save the changes.
WordPress will display your password protected post differently. Protected: will be added before the post Title and instead of the post content it will show a password form. Only people that you provide the password to will be able to view that post.
There are many other ways to set the visibility for your blog content. You can also make your entire WordPress blog private through the use of WordPress Plugins.