You can download the game by clicking "Download" button based on whether you own a PC (Windows) or a Mac. Unless you have a pop up blocker, it should download automatically.
Then, I believe you can follow MedicXBombs's steps if you have a PC. For Mac users, it should be easier, since you can just double click on the zip file to unzip it, double click the unzipped file, and it should launch the game! :)