i downloaded the zip but i dont know what to do next, can somebody please tell me how to do it step by step, that would be very cool...

Unzip the .zip file into a folder. Open up the Zero Deaths folder, PC, and double click on the Zero Deaths.exe file.

(If you use a Mac, go into the Mac folder instead of PC and double click the Zero Deaths.app file, or move the Zero Deaths.app file to your applications folder)