Hmmm... I would have said that Ubuntu is a Linux Distribution
as is Red Hat, Suse, Mint, Mandriva, etc. The operating system is GNU/Linux. A distribution doesn't just have an operating system, it comes bundled with Applications to handle documents, spreadsheets, photo manipulation, presentations, drawings, you name the job, there'll be some application to do it.
The applications are common to most distributions and can be added to using package managers which may be particular to the particular distribution. Different distributions have different ways to manage them, different windows management, etc, you find one that you like and start there.
Note that an OS like Windows needs you to buy the applications and install them, on its own it's pretty useless and can't do much. Ubuntu, etc installs apps along with the OS, GNU/Linux.
Well, anyway, thats my