I downloaded this because it looked so fun, how do I save it?
If you're referring to saving it to your computer:
Once you click the download button, open the file that was downloaded and drag the "Grape Escape" folder anywhere on your computer. From there, you can open the folder and click the "Grape Escape" application to play it.
If you're referring to saving the game's progress:
It should autosave every time a new scene is loaded (i.e. main menu, upgrade lab, etc.), so you won't have to worry about lost progress. :)