Random Warning Thingie at the top of my page?!?! What is it? (Ex. in message)

(SEE BELOW) I have this at the top of my page- can anyone tell me what it means or how to get rid of it? I am not very computer savvy, so if possible could you use the simplest way of explaining please? It would be very much appreciated! I’ve been trying to add an audio player to my page for about three days straight with no success- I’m not quite sure what I did to create this mess- but I’m going completely crazy! If anyone has any ideas or suggestions it would be a step in some direction, because I seem to be going in complete circles and my website totally sucks!?!?! Thanks for any/all help ?? ~C.

Warning: Cannot modify header information – headers already sent by (output started at /home/content/49/6559849/html/wp-content/plugins/audio-player.php:905) in /home/content/49/6559849/html/wp-includes/functions.php on line 830

Warning: Cannot modify header information – headers already sent by (output started at /home/content/49/6559849/html/wp-content/plugins/audio-player.php:905) in /home/content/49/6559849/html/wp-includes/functions.php on line 831