If you have exported your WordPress contents as XML file or have WordPress theme’s demo content file as XML, You can easily import that into any of your WordPress site.
So how can I import?
First login to your WordPress admin panel then follow below screenshot.
Click on ‘Import’ see in green circle under ‘Tools’ menu, it would open a page like what you seeing in right column. Now click on ‘Run Importer’ showing in red circle. It will open another page where you have to just choose your XML file, then click on ‘Upload File and Import’ Button. You are now done.
If you like to export your WordPress content in to a XML file see this article here.