Use a program like winrar or 7zip to extract the files. I personally used 7zip and the game runs fine.
Edit: spelling
Edit 2: The new update (v0.5.8) has now made the download a zip file rather than a rar, so you no longer need either of the above programs. Now you just right click the download and click extract all.
Uuuh... never tried doing a step-by-step through text before, so I apologise if anything is hard to follow. Also sorry for the late-ish reply.
1. download 7zip, just look it up and it should be the first site.
2. right-click the game file, and select "open with..."
3. you will see a menu appear with a bunch of apps. First, make sure the check box to always use the program is ticked, then click "more apps", then scroll to the bottom and click "look for another app on this pc"
4. locate where you downloaded 7zip, it should be very close to the game file. You'll want to select the 7zip file manager. It might be called 7zipfm.
5. 7Zip will now open the file, now just click "extract" to access the game
This assumes you are using windows. I don't use other platforms myself, so you'd have to ask someone else if you do.
