Hi Titanic
I have Ubuntu on a DVD, I pop it in and boot up.
The OS is all on the disk, and doesn't have any components on my PC.
Even if Windows is totally borked it will start almost any any computer, and let you access your files, get online, get to a forum for help etc.
It has a built in browser, word processor file manager etc.
I've used it many times to backup data, on a non booting computers, mine and other people's before reinstalling.
It has also let me solve issues with things that Windows for some reason won't let my access, like a file it won't let me delete.
It's great having the disk around, you can always use it as a last resort, to get into a crashed computer.
It's worth the time to make a disk just in case you need it some time.
http://www.ubuntu.com/download/desktop Check out the take the tour button...
http://www.ubuntu.com/desktop/take-the-tour The disk can be used to install Ubuntu on your PC as well, but I've never done that, I just opt to run it from the disk.
For someone who only wanted to do the normal things like email, word processing, browes, watch videos, or listen to music, it could be your only operating system, the problem comes when you want to run other software like Photoshop or games like Skyrim, it's either a hassle or impossible.
Mike