VirtualBox overview
If you would like to try Ubuntu (or other Linux, Solaris, BSD or Windows OS without affecting your main machine or if you want to test something on Ubuntu (or other OS) in a safe environment instead of on your native install, with VirtualBox you can create a virtual installation within your current OS
Installing VirualBox
Ubuntu host
Open a terminal (Crtl+Alt+t) and run the following command
sudo apt-get update && sudo apt-get install virtualbox
Windows host
Download a copy of VirtualBox.
Once your download of VirualBox for Windows has completed you will have a 'Executable File' (.exe).
'Double Click' the .exe file to initiate the installation.
Mac host
Download a copy of VirtualBox.
Once your download of VirualBox for Mac has completed you will have a 'Disk Image File' (.dmg).
'Double Click' the .dmg file to mount its contents.
A window will open, 'Double Click' the VirtualBox.mpkg file within the window to initiate the installation.
More installation info can be found on the VirtualBox website manual.