First you must login to MySQl as root

then select the database mysql

use mysql

Then apply the user and password to the database of your choice

Grant ALL PRIVILEGES ON database_name.* TO username@localhost IDENTIFIED BY "password";

This grants username access to all tables under database_name.

Now we have to update privileges for this user

update user SET Select_priv='Y', Insert_priv='Y', Update_priv='Y', Delete_priv='Y', Create_priv='Y', Drop_priv='Y', Reload_priv='Y', Shutdown_priv='Y', Process_priv='Y', File_priv='Y', Grant_priv='Y', References_priv='Y', Index_priv='Y', Alter_priv='Y', Show_db_priv='Y', Super_priv='Y', Create_tmp_table_priv='Y', Lock_tables_priv='Y', Execute_priv='Y', Repl_slave_priv='Y', Repl_client_priv='Y'  WHERE User='username';

For security you should limit the 'Y' to Insert, Select, Update unless this is your super user.