I have two DVDs. I cannot install from either. One is xxx.iso the other contains files: .disk, boot, casper … etc
What should I see if I display the files that are on a proper DVD?
Boot from the DVD that contains the Ubuntu 18.04 .iso image (ubuntu-18.04-desktop-amd64.iso) burned on it with a CD/DVD burner. For more information about how to burn an Ubuntu installation DVD on Ubuntu read How to burn an Ubuntu ISO image on a DVD on Ubuntu?.