One thing to note first: The docker image just named "mysql" is maintained by Docker, not Oracle. The Oracle-maintained image is named "mysql/mysql-server". They largely have the same features, but may differ in some ways.
As for the database import, you don't actually have to do anything for that aside from copying over the database files (plus any custom config you might be using). We don't recommend actually storing data inside the container, but instead mapping the database location to one on the host. There's some detailed information about it here: https://dev.mysql.com/doc/refman/8.0/en/docker-mysql-more-topics.html#docker-persisting-data-configuration
Say you have the data copied to a location /somepath/mysqldata on your Docker host, then in step 2 above simply add the following after "docker run":
(The MYSQL_ROOT_PASSWORD option is not needed when starting up with an existing database)
You should now be able to log in with «docker exec -it some-mysql mysql -uroot -p»