Add/Remove mysql users..

add Users and Password

GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY 'password' WITH GRANT OPTION;
GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY 'password' WITH GRANT OPTION;

remove users

mysql> show grants for idiot@localhost;
mysql> revoke all privileges, grant option from idiot@localhost;
mysql> drop user idiot@localhost;FLUSH PRIVILEGES;