You can import your database by following the guide on upgrading from an earlier version (http://xibo.org.uk/manual-tempel/en/upgrade.html#switching_to_docker). The container is setup to look for an import.sql file.
If you want to have PHPMyAdmin available to you, you can do so by running it in it’s own container. That’s covered in the following FAQ:
Your custom HTML goes in shared/cms/userscripts and is available at http://server.domain.com/userscripts where server.domain.com is the IP address or DNS name for your server.