We are using here Ubuntu because it's certainly the easiest-to-use Linux OS (distro). Besides, most of the stakepool content you will find online is made for Ubuntu. You can find more understandable info about Ubuntu on the simplified Wikipedia page here.
2.1 Close the "Settings" page and click on "Start"
2.2 Choose your language, and click on "Install Ubuntu"
2.3 Choose your keyboard layout and click on "Continue"
2.4 Select "Normal installation"
2.5 Select "Download updates while installing Ubuntu"
2.6 Click on "Erase disk and install Ubuntu"
4.7 Click on "Install Now" and click on "Continue"
4.71 Choose your region and setup a username and password
4.8 Complete the installation
4.9 | Restart the virtual machine by clicking on "restart" and wait 30 seconds
If Ubuntu doesn't go in full screen mode, follow the following steps:
Go the terminal by clicking on the 9 dots on the left of the screen
Search open "terminal"
Execute the following in the Terminal:
sudo apt-get update
Now wait a few seconds and click on "Devices" and then on "Insert Guests Additions CD image..."
Then click on "install", wait a few seconds, and now you should be able to have Ubuntu in full screen.