Cannot modify header information – I can't get to my admin panel

Hello,
I was about to finish installing the wordpress files, wrote down …/wp-admin and then the message like that occured:

Warning: Cannot modify header information – headers already sent by (output started at /rswww/wp-config.php:1) in /rswww/wp-includes/pluggable.php on line 881

I tried to get rid of the free spaces in the file what I read could be a reason of the problem. It didn’t help, though.

Do you have any clue?

Thank you for your help.