Installation
gentoo ~ # emerge dev-db/mysql
Configuration
As this is a new install, we need to initialize the databases:
gentoo ~ # emerge --config =dev-db/mysql-[version]
Start the MySQL server and check /var/log/messages for any errors.
gentoo ~ # /etc/init.d/mysql start
If everything seems OK, add MySQL to the default runlevel.
gentoo ~ # rc-update add mysql default
Discussion
There is really not much to discuss regarding MySQL, apart from the fact that many programs can make use of it as the standard database. If you want them to do so, then add mysql to your global USE flags in /etc/make.conf.