VirtualBox allows users to install multiple guest operating systems on a single machine. The document outlines the steps to install VirtualBox and then install Ubuntu 13.04 as a guest OS. It describes downloading and installing VirtualBox, creating a virtual machine, configuring settings like memory and storage, and then walking through the Ubuntu installation process by selecting options and components. The summary provides a high-level overview of the key steps involved in setting up Ubuntu as a virtual machine on VirtualBox.