Cannot Modify Header Information

Hi everyone! I already installed WordPress successfully and when I login, about 8 warning messages appear on my screen. Here’s one of them:

Warning: Cannot modify header information – headers already sent by (output started at /home/usernamehere/public_html/wordpress/wp-config.php:23) in /home/usernamehere/public_html/wordpress/wp-login.php on line 7

And the list goes on! I don’t know what’s wrong! I checked my MySQL database, username, and password..they’re all correct! But I still get these warning messages! Does anyone know how to solve my problem?? HELP!!