You may want to disable access to your website to all users (for example when you are changing important pages on your auction site). To do this, you should enable Maintenance mode. Make your pointer click on the second icon from the bottom in Admin Panel and click Maintenance mode.
Click the Enable maintenance mode button.
From now on, users won't be able to access your site. To turn the maintenance mode off, go back to the same panel and click the same button which will now show the text Disable maintenance mode.