Installing DayZero and fixing any problems

Install Arma 2 and run it once.
Install Arma 2 Operation Arrowhead and run it once.

Your Arma 2 Operation Arrowhead needs to be the latest version and do not opt into the beta version.

How to install DayZero and fix any problems

DayZero launcher install link: https://launcher.zombies.nu/setup.exe (https://zombies.nu/ bottom of page if you prefer to download that way)

Use this launcher to install the files by clicking on the versions tab.

It should look like this once installed: http://i.imgur.com/7Hu4BcX.png

Common Problems:
DayZero.dll is missing: https://zombies.nu/community/threads/12066/
Whitelisting problems: https://zombies.nu/community/threads/12066/
Output path empty: Start arma 2 and arma 2 oa to the menu and exit, also verify files.
An error occurred while trying to resume your session. Please try again: If you get this after rejoining the server after a restart, wait 2-3 minutes and try rejoining again.
Initiating authentication: Restart steam and try relaunching the game again.