If you want to put your site on hold or on maintenance mode, You can use maintenance plugin to put your site on maintenance mode.
WordPress provide so many plugin for maintenance but in this blog we use WP Maintenance Mode.
Lets start ,
Step 1 : Go to plugins and Add new.
Step 2 : Click on install button and activate it.
Step 3 : Go to plugins and setting of WP Maintenance Mode.
Step 4 : Activate the status and save setting.
Step 5 : Now refresh your site you will see your maintenance mode is activated now.