These virtual computer is hidden because its running inside the current running operating system on your desktop/laptop once you set it up.
Having a Virtual Machine can be very helpful and beneficial especially when a new Operating System comes out and you would first like to Try It Before You Buy It such as Windows 8 for example!
If a new Operating System comes out how could you decide if you like it or not unless you try it out. Unfortunately most stores offer just a demonstration with a Commercial User Account and Limited functionality and user control. You want to fully try it out and learn it as if you already own it!
But allot of times allot of inexperienced computer users risk trying it out by fully formatting their entire hard disk on the computer and delete everything that they know how to use and navigate on.
What happens if you don't like it? How do you go back to the way it was? Do you have to buy the Operating System all over again if its not a free version Operating System like Linux? If you purchased the Operating System again since you skipped to make recovery disks, how do you re-install it? Once you re-install it, are all the devices installed with it as well? If all the computer hardware/devices are not installed yet where do you find the DRIVERS for them? If the most important DRIVER like the Network Card is not installed with windows re-installation how are you going to connect to the Internet to download the rest of the device drivers?
Do you see where this is going? The headache is limitless and the list problems is endless!
This is where the virtual machine saves your day, because it gives you the chance to try it before you buy it if we are talking about Microsoft Windows! You could also Try it before you Decide it if you are trying Linux!
As long as your main computer is running a 64bit OS and has over 4GB of RAM (Randomly Accessed Memory) then you can test out any operating system of your choice. Learn to use it to the max in the Virtual Machine before you can feel fully comfortable to move forward to format your main computer with the new Operating System of your choice as the new default OS. Maybe even Better to Stay where you are with the current operating system that you might be using as long as its not out of technical support and still secure for you to use!
This will better help you decide if it's worth buying a new computer with a new Operating System on it at all!
Now if your computer is running with 32bit Operating System you can still install the Virtualbox and still test out some operating systems but don't expect the performance to be fast and stable and make sure you have no less then 3GB memory and don't try to add more because 32bit Operating Systems can't read more then 3GB memory even if you added 16GB memory unless you are running Linux as the hosting Operating System!!!
My favorite Virtual Machine software is called Oracle VM VirtualBox and the best part is that its FREE! Once you download the VirtualBox you can set it up and try it out like I have been using it out since 2007.