itch.io

Click the Download button that has your OS next to it, right click the downloading file in the bottom corner, click Open when done, click on RanitaFishing, click the middle file that should also be called RanitaFishing, click, "Extract" (It may open another window asking you to hit extract again), then once its done extracting, on the window that opened after the extract, click RanitaFishing then click the middle one again, if a Windows security window pops up, click More Info, then hit run anyway.
P.s. I'm on Windows 10 so if your on Mac it will most likely be different for you