There are a lot of options for downloading Linux. My suggestion is to start with Mint. It's probably the easiest to use for beginners, and intermediates as well. It also seems to support the most hardware. You can download it by using the link at the top of this webpage, Download Linux. Unfortunately, once you get to the Mint page, you have to choose which desktop you want to run. If you have an old computer, you might want to try the XFCE desktop. If you have a newer computer then either of the others will work well. Just do a eany, meany, miny, moe to choose
One of the many great things about Linux is that it's free. And versatile. So if you don't like the desktop you choose, or the distro, you could download another one (desktop or distro). So if you choose Mate and later decide to try Cinnamon, you have nothing to lose, just download the desktop and switch over. You can switch back and forth after downloading the second.
But before proceeding too far, you need to take Condoblokes questions into consideration. What are your plans, dual booting (keeping Windows and installing Linux also), or wiping out Windows and having nothing but Linux? Do you need to keep any docs? One option you have is to download it to the USB and only run it from the USB for a while till you make a decision. There are options to do this and keep any settings that you change on the USB. You'll need to let us know these answers and we'll be glad to help you out.