And yes, for any reason we always have a backup of what we can't lose. Hard drives fail all the time and some folk are not prepared.
http://www.ubuntu.com/download/help/install-desktop-latest does not go into great detail but the last time I did that I did not have to partition the drive. I select the option to install Ubuntu alongside the install OS and the installer made the room for me.
Some folk don't try that and lose weeks or months trying to partition when if they had gone ahead and followed the directions they would have been done.
I want to partition the hard disk since there is just one volume C ( OS) and install ubuntu also. Do i need to take a backup of my data? Also, does another volume contain the new OS ubuntu?