most games on this website require files such as 7zip to un-compress them, you really only need to download like two things, 7zip or WinRAR (WinRAR has a free "trail" that never ends due to copyright/ piracy prevention issues etc), either way you should already have at least one installed if your planning on purchasing anything from itch.io
Once you've downloaded 7zip or WinRAR you need to download the game file, move it to your desktop, right click it and click extract with WinRAR or 7zip, the files should then extract to your desktop, you can open the extracted files and open the .exe file.
If you have a Mac or Linux the Program won't work due to it only being windows based, you can try to contact germ food via twitter and get a refund, or even itch.io itself, but non of these garentuees your refund of $1.93 USD.