Because the script wasn't originally intended to be distributed it isn't hugely documented, but here's a brief setup guide:
1/ Unzip the .zip file.
2/ On your web server, run the SQL commands in feedcombine.sql through a MySQL management tool such as PHPMyAdmin online or Sequel Pro if you're a Mac user.
3/ Update all of the settings in settings.inc.php - these are annotated. If you don't update the siteaddress setting then the script will fail to redirect to the correct place, and obviously you need to update the database settings!
4/ Upload all of the files in the .zip file (except for feedcombine.sql) to your server.
If you've enabled logging in the settings then you'll need to set up a cron job to run cron.php every 24 hours to generate the report. Enabling logging will also limit the number of views on any given combined feed for any given IP to 300 per day. If you want to do this manually, you can load stats.php - the default password is defined as "statsaccess" without the quotes.
I do ask that you keep the FEEDcombine logo at the top, and the link back to my web company at the bottom of the feed generator page.
Finally, just to confirm, I'm making the script source available on an as-is basis. I'm afraid I can't offer any guarantees that it'll work on your server, or that it won't affect the server load (it shouldn't through normal use, obviously, but if it does then I'm afraid I can't take any responsibility for this). To reconfirm: I can offer no guarantees related to how it'll work and any effects it has on your server are entirely your responsibility. By installing and accessing the script, you accept this is the case.
For more information, please email firstname.lastname@example.org. But please note I'm not able to offer case-by-case support for the script.
To download the script, indicating you accept the terms above, click here.