This tutorial will show you how to put the Drupal website in maintenance mode.
1) Login to your admin panel.
2) Go to Configuration
3) Scroll down and click on "Maintenance mode" button
4) Match the option "Put site into maintenance mode". You can edit the maintenance mode message here. It will be displayed on the Maintenance page
3) Check your website now.
Feel free to check the detailed video tutorial below:Drupal. How to put the website in maintenance mode,