Hmmm, do you have a downloads folder? I'd recommend searching for a file called CrimsonHydrangea-0.1-mac.zip . Once you've located that you can right click and click " open with" and select "archive utility" in order to unzip that file. Then once it's unzipped, you should see a new file appear labeled CrimsonHydrangea and once you double click the game should start playing.
If it still doesn't work I'd recommend either downloading or troubleshooting with https://www.renpy.org/ to make sure that it's compatible with your mac.