Maintenance mode is used when you need to make some changes to your OpenCart store and you want to disable the functionalities of your website for the public in the meantime.

To do so you first need to go to the Dashboard of your application.

Then you need to go to System > Settings > Edit button next to your store:

The next step is to go to the Server section of the menu. On the top you will see the Yes/No options for the Maintenance Mode:

Once you choose the option you want to apply you just need to click the Save button.

If you enable the maintenance mode (select the Yes option) the visitors of your website will see the following screen:

To disable the maintenance mode you will once again need to go to the Dashboard > System > Settings > Server section > Select the No option of the maintenance mode.