In the lab page of your ghost dashboard you can find an option section named "Migration options". using options in this section you can import, export or delete site data.
Use this option to import new data into your ghost installation. Maybe you have exported data from a ghost installation and you want to import that data into another Ghost installation. You can use this option to do this.
May be you had taken a backup of your site data at earlier point of time and you need to restore the site to that point of time. That too is possible using this option.
You want to take a backup your entire site database. There is an export option for that. Just click on that export button and a .json file will be downloaded which will include your site's entire data.
You can also keep this json file as your site backup.
Delete all content
Normally in most of the site life-cycle, you probably never want to delete your site data permanently. But in case situation like this ever come, you know what to do. Just click the delete button and all your site's posts and tags will be deleted.