vimtutor is a program that usually gets installed when you install the normal vim/gvim package. You should be able to just run "vimtutor" on the command line, assuming that it got built and installed correctly, and is on your path, etc... If you can't run it on the command line, or it doesn't work for you, you'll have to do some digging to figure out why. In my experience vimtutor doesn't always work as expected. I would start by looking in the install folder for Vim, and see what you can find.
At its core, it's basically just a text file that has some examples that walk you through the basic commands available in vim. It shows you have to navigate using the keyboard, how to edit text, and use some other basic commands. If you can't get vimtutor to work immediately, you can either just keep messing with it, do some more searching (there are plenty of results when you search for vimtutor in google) or just give up on it and learn vim using another type of tutorial. Vimtutor is fairly limited anyway, so it's definitely not that important to get working.