pc: extract the zip. there should be a .exe file for the game, open that to play it
mac: idk
android: open the apk file. your phone (or tablet) should ask you if you want to install it. if it google stops you from downloading it, select the "advanced" dropdown, then 'download anyways'. If you don't get an option, make sure the browser you're downloading on has the 'install unknown apps' setting enabled in your system settings, as the 'install instructions' section of this page says. then once all of that's done, your device should give you an option to open it after it's done installing. Tap that if you wanna start playing immediately, or cancel if you want to play later (you can find it again by opening your app dock)