My second Ultimaker 2 video, in which I download STL files, use the Cura slicing software to convert them to G-Code, and create 3D prints. My first Ultimaker 2 video -- that you may like to watch before this one! -- can be found at:
https://www.youtube.com/watch?v=TgS8202tQEI
More videos on computer hardware and related topics can be found at:
http://www.youtube.com/explainingcomputers
I also have many more printing videos on my other channel at:
http://www.youtube.com/explainingthefuture.com
You can also learn more about 3D printing in my book "3D Printing: Second Edition", the first chapter of which can be downloaded as a free pdf from:
http://explainingthefuture.com/3dp2e.html