The PCB fab files contained in the ZIP file are what was sent to the board house (www.SilverCircuits.com) to fabricate the board. They have been provided for reference, but you will need to find a free Gerber viewer to view the files.
Some free Gerber viewers are:
If you want to have a board fabricated, these files will be accepted by just about any PCB manufacturer, but be aware that the cost for a single or small quantity of PCBs can be expensive! It is best to order in quantity. See the Turnkey Interface Page for ordering/waiting list details. Also, you will want to edit the contact information contained in the Readme file before placing an order.