Open up the Google Drive web interface.
Go to New - More - Apps Script
Paste the above code in at the top, above the myFunction it automatically creates.
Change myFunction to something like this:
Code:
function myFunction() {
listfolder("The Folder I Care About");
}
Save the script (you have to actually click on the floppy disk icon), and run it (the play button). It will ask for permission to access your Google Drive, then it will run for a minute. When it's done running, you should have a Google Sheet with the same name as the folder, plus a long string of numbers. That sheet should contain a list of all the files in that folder, and their URLs, if you keep that part of the code.
More on Apps Script at
https://developers.google.com/apps-script/overview .