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.