It's really easy on windows. You don't need winrar, you can extract it with windows as well. Right click on the downloaded file -> Hover the "open with" entry -> Click on "windows explorer".
A new window should come up with a directiory inside. Drag and drop this directory on the desktop(or another location of your choise).
Close the explorer window.
Open the directiory, which you dragged on the desktop.
Double click the "AncientWarfare2.exe" file to start the game.
Greetings to your grandson!