I am not a tech guy. Here is my layman's terms explanation.
Computers don't usually come with a stock program that open these files. A program needs to downloaded to open a RAR file.
I recommend get 7-Zip. You can download it at:
Also I found used this wiki how guide. It was very helpful:
https://www.wikihow.com/Open-RAR-Files
I haven't downloaded the game on my phone so I haven't opened a APK. But here is a wiki how guide to do it:
https://m.wikihow.com/Install-APK-Files-from-a-PC-on-Android
If you need more help feel free to message me again.