Adding and Removing Privileges:       [See in MySQL Manual 4.2]
To add user privileges use the GRANT command:
GRANT privileges [columns]
ON [ * | *.* | dbanme.* | table_name ]
TO user_name [ IDENTIFIED BY 'password' ]
[ WITH GRANT OPTION ]

To remove user privileges use the REVOKE command:
REVOKE privileges [columns]
ON [ * | *.* | dbanme.* | table_name ]
FROM user_name

A list of Privileges for Users:
SELECT, INSERT, UPDATE, DELETE, ALTER, CREATE, DROP
Note: If wishing to allow a user access to all privileges use the key word 'ALL'

Reloading the User Privileges:
If you have add or removed any user privleges you must reload the user privileges or MySQL will not see the changes.
C:\mysql\bin> mysqladmin reload
or from inside mysql
mysql> FLUSH PRIVILEGES;

Examples:
Grant all privileges on all databases to a user called Fred.
mysql> GRANT all
mysql> on *
mysql> to fred identified by 'hi1234';

Grant all privileges on a database called 'webpc' to a user called Fred.
mysql> GRANT all
mysql> on webpc.*
mysql> to fred identified by 'hi1234';

Grant select, insert, delete and update privileges on a database called 'webpc' to a user called Fred.
mysql> GRANT select, insert, delete, update
mysql> on webpc.*
mysql> to fred identified by 'hi1234';

Revoke all privileges on all databases to a user called Fred.
mysql> REVOKE all
mysql> on *
mysql> from fred;