To set the root user password. From terminal.
/usr/local/Cellar/mysql/5.5.20/bin/mysqladmin -u root password 'enter_a_password'
Then do
mysql --user=root --password=enter_a_password
In the mysql command prompt:
For DB_NAME, ENTER_DB_PASSWORD, ENTER_DB_USER, enter values of your choosing.
create database DB_NAME;
grant all on DB_NAME.* to 'ENTER_DB_USER'@'localhost' identified by 'ENTER_DB_PASSWORD';
flush privileges;