

In the "Optical Disk Selector" window, click on the ISO image you just downloaded and hit "Choose". Then pick the ISO image you just downloaded and hit "open". If the ISO image you just downloaded isn't already visible, hit the big green plus sign ("+") to bring up a file chooser. Hit the little folder icon next to the drop-down box to bring up the "Optical Disk Selector" window.


Click on the icon for that virtual machine ("testUbuntu20") and hit the big green arrow "Start" icon.(Optional: If your purpose for setting up this machine is to practice installing Ubuntu on a RAID array in a safe sandboxed environment, set up additional virtual hard drive images now under Settings > Storage).Hit the "Next" or "Create" button a few times (2048 MB RAM, keep the default 10 GB hard drive file - you can make these bigger or smaller later), until you see an icon for your virtual machine in the left sidebar of the Oracle VM VirtualBox Manager.The default is 1024 MB RAM - bump this up to at least 2048 MB RAM for Ubuntu 17.10 or later.Remember, this is the guest operating system running inside the virtual machine, not your host operating system). (Many people give woefully uncreative names like "testUbuntu20") Start the Oracle VM VirtualBox Manager.Don't wait until it is done, which may take a few minutes - continue with the following while it's downloading.

For example, you may want to try Ubuntu Desktop 20.04 LTS.
