Go to Distrowatch.com (look around and see what you like) and download a linux distribution (operating system). I would highly recommend this to anyone who is not a super professional that needs Windows for very specific software. Since you are a beginner, it would be best to start with a much simpler distro and then move onto harder stuff if you so desire. If you need any further help or recommendations with books or links to websites just PM me.
Plus the installation of it has been become so easy, and the learning curve has greatly been reduced. I would advice you to download Ubuntu, or try a live CD and see if you like it. Depending on what sort of hardware you have you might want to download XFCE
(lighweight desktop) or KDE
which is a full desktop experience very similar to Windows.
Here are the specific links, my best wishes to you! +Pax+
You can download a bittorent client to download it even faster, I would recommend an open source one like deluge
After the downloading the image, either use a USB or a DVD to burn the iso file
. Now you can look at this website
to help you decide which one you want. I could recommend this one for windows, just make sure whenever you install it from Windows to make sure to not click blindly next, because it will ask you to install some pretty stupid stuff (I hate this with free windows software). In Linux you never have to worry about malware, spyware in your software, because you download them through package manager's or even better from source (cryptographically secure downloads through a source repository). So you don't have to worry about all that crap! That website can also help you find some alternatives to commercial or open source software.
Hope that helps!