If I take the steps as in the title, I end up in a window called:- x@x-Not-Specified:~ What can I do with this application? What is it used for? How can I learn about it?
You have started a Terminal program, which gives you access to the Linux command line, similar to the old DOS Prompt or Windows'
cmd shell, where you can type in commands and receive information in a text-based format. Expert users can do just about any computer-related task in this environment, but it can be extremely important even for first-time or casual users of Linux operating systems like Ubuntu. You can use it to quickly install, upgrade, or remove packages, manipulate files and folders, check your network connection status, and many more tasks.
Ubuntu is designed in such a way that the command line often isn't necessary for day-to-day use of your computer, as there are graphical programs such as the Software Center or Nautilus, the file browser, that manage many of these routine jobs. However, if you are interested in learning more, there are many resources available to check out. If you'd like a physical book to put on your desk (or even an ebook to put on your tablet), you can't go wrong with Linux in a Nutshell, which I've had for many many years and still reference occasionally. The first link I provided links to a number of online tutorials for learning the command line (also known as
Bash or "the shell").