Yeah that means there is an error in your php code somewhere. Since it could be anything, anywhere, I have no idea what it is exactly. If you can, try and undo whatever code you’ve added and see if that fixes it. Then you can see exactly whatever the issue is.
I assume you’re using FTP to do all of this right? If so, disregard the following……If not, I would highly recommend you do just in case you make a mistake. If you use the WP editor and make a php error, you’ll get a white screen with the error, and your entire site will go down until you fix it. If you use FTP all you would have to do is “undo” whatever mistake you made and the site would return back to normal.