Which operating system?
The downloaded file is a ZIP file of a folder. You need to unzip that somewhere on your PC and then inside of the folder is an Evolution.exe file, which you should be able to double click in order to start it. Let me know if that doesn't work and if so, what happens instead of Evolution launching.
I haven't used the itch.io launcher myself but I suppose that would simplify all of this to just downloading Evolution through the launcher and then clicking "Launch" in there. You could also try that.
is it possible that you can find a way to not have a paywall against the windows version? my family is very low on money and i really just want to play some cool game to pass the time without having to pay. please find a way to fix this, its kind of lying about it being free if you have to pay just to get a windows version. thank you!
There's already a way to get it for free. The entire source code is available here: https://github.com/keiwando/evolution, so you can download it and download Unity (also for free) and build the windows version yourself.