Those are docker questions that are independent from XWiki.
You need to read the doc for “docker run” at Running containers | Docker Docs to understand the parameters passed.
You really need to read carefullly the doc at https://hub.docker.com/_/xwiki/ it has all the information.
For example:
The command below will also configure the MySQL container to save its data on your localhost in a /my/own/mysql directory:
docker run --net=xwiki-nw --name mysql-xwiki -v /my/own/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=xwiki -e MYSQL_USER=xwiki -e MYSQL_PASSWORD=xwiki -e MYSQL_DATABASE=xwiki -d mysql:5.7 --character-set-server=utf8 --collation-server=utf8_bin --explicit-defaults-for-timestamp=1
You should adapt the command line to use the passwords that you wish for the MySQL root password and for the xwiki user password.
I think you need to read docs about Docker first. Or not use Docker: there are other ways to install XWiki.