Hello,
Thanks for the question about putting your site in maintenance mode. Typically, if you're using an application like WordPress to build your site, then you can load an add-on that will provide a maintenance mode with the ability to allow certain users through to the site. Otherwise, you will need to restrict access to the site using the .htaccess file and IP Deny Manager in cPanel. I hope this helps to provide you enough information to allow a preview of the site to only a select few.
If you have any further questions or comments, please let us know.
Regards,
Arnel C.