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Hello, I need some help. I was able to download the "win64.zip", but I don't know what to do next. Please help me!

You have to open the .zip file with a program like winrar or 7zip.
Extract the files there to a choosable folder and (most likely) klick the.exe file in order to play.
But first yo need a program that can open .zip files.
Doesn't really atter which one you take, but be aware that the free programs are already enough.
No need to pay money for such a program.