As it says on the tin
Create the user
mysql> create user mysqlusergoeshere@localhost identified by 'somepasswordcangoheremakeitsecure'; Query OK, 0 rows affected (0.03 sec)
Create the Permissions for the user
mysql> GRANT ALL PRIVILEGES ON database_name.* to mysqlusergoeshere@localhost; Query OK, 0 rows affected (0.01 sec)
Simples.
This can also be put in the one command:
GRANT ALL PRIVILEGES ON database_name.* to mysqlusergoeshere@localhost identified by 'somepasswordcangoheremakeitsecure' ;