The file is a .rar file. It is free and easy to unpack. If you are having trouble opening check out this link
Watch the Video for the Infinity Cube build here: https://youtu.be/0sDKh_3uEuY
My friend at Everything Wood and Metal has a great cube calculator if you want to do a different size than I did. Check it out here: http://bit.ly/InfinityCubeCalculator
These are some supplemental documents you can print to help wrap your head around tackling something like this.