We've installed your MySQL database without a root password. To secure it run:
mysql_secure_installation
MySQL is configured to only allow connections from localhost by default
To connect run:
mysql -u root
To start mysql now and restart at login:
brew services start mysql
Or, if you don't want/need a background service you can just run:
/usr/local/opt/mysql/bin/mysqld_safe --datadir\=/usr/local/var/mysql