Once you open the game's folder you're going to see a file with the name "CasualtiesUnknown.exe" right below the folder "MonoBleedingEdge", generally, ".exe" files are executables, meaning, they open programs in your pc :)
it should be on the main folder, it's got a little image with some light blue in it, i wanted to show you some images as a guide but it wont let me, if anything, you can find tutorials that'll teach you a bit more about computer's interface and such
Also, when you find the .exe file, double click on it, it should open the game right up c: