>What is supposed to be used to open 7z files and why the name includes kor? I downloaded the advanced 64 bit version but don't know what to do with it. I have no default program opening the 7z files.

Everyone should have / get 7-zip :)
It does zip, 7z and everything else. It is good. And free.

https://www.7-zip.org/


The 7z format is smaller that zip.