My SQL Username

How do you find your MySQL username? I have my password, but keep on getting the same message:
Error establishing a database connection! This probably means that the connection information in your wp-config.php file is incorrect. Double check it and try again.
Are you sure you have the correct user/password?
Are you sure that you have typed the correct hostname?
Are you sure that the database server is running?
I don’t know how to access Php either, I installed it, but don’t know anything about it.
Thanks.