First create user:
CREATE USER '<username>'@'<host to connect from>' IDENTIFIED BY 'clear text password>'; or CREATE USER '<username>'@'<host to connect from>' IDENTIFIED BY PASSWORD '<encrypted password>';
Grant some rights to the user (here all as * is used):
GRANT * ON <database name>.* TO '<username>'@'<host to connect from>';
Put privileges into action:
FLUSH PRIVILEGES;
Check MySQL documentation for more details.