After the demo content import, you will a page with a clear message: "All done!" If you install the demo content and after your page stop to load and you can see only the WordPress admin area without content or you get an error message like "Error500", Read more

Please go to WordPress admin -> Tools -> Import -> WordPress. Then you have to install the plugin "WordPress Importer" (https://wordpress.org/plugins/wordpress-importer/), just click the "Install now" in the pop-up window. After this, you have Read more