7z is a type of file compression used to make so stuff like games take up less room you to uncompress or unzip it to its own folder in order to use it there are apps that do this such as winzip bandizip izip. Download the app install it then download the game if you havent and right click it and select either extract to HoleDweller42 or unzip to HoleDweller42 or uncompress HoleDweller42 and open the folder it just made and double click on the exe in the folder. Hope this helps