You can download the Ubuntu 24.04 ISO image from the link above. It’s over 5GB, so won’t fit on a regular DVD. Unless you’ve got a thing for dual-layer optical media, you’ll want to write that image to a USB drive.
This is more complex than just copying the file on to it, and you need specialist tools to do it. If you’re already running Ubuntu, it includes its own tool for this, called Startup Disk Creator.
Otherwise, we recommend Etcher, which you can get from https://etcher.io. It runs on Windows, Mac OS and Linux. Fire up Etcher, select the ISO you just downloaded and hit Flash. Now make a cup of tea while it’s writing.