Real time zombies/shooting

Hey Guys, So i'm trying to create a zombie survival game where the game has a real time shooting system. I have the tiles for the zombies (I believe) but the problem is i don't know how to have shooting in real time. I don't know if i'm saying it right but basically I want to have a shooting system like in this video.










I want to know how I can be able to make a shooting system like the person has on this game. It will be like my dream. What script do you need. What else from that do you need. How do you do it. Etc etc. Please help guys. My game is only missing the shooting system and real time enemy system. I was also wondering if there is a day and night time system as well. Thank you so much!


Btw: This is the zombie sprite i have now.