what recovery are you using if not TWRP I would switch.
1. download twrp from this thread
http://forum.xda-developers.com/showthread.php?t=1782235 put it on your sd card and flash with your current recovery. reboot
2. download bb8 and the GappsInverted-unified zips and put both on your sd card (root is easiest for beginers)
3. reboot into twrp recovery
4. select back up and back up your current system
5.select wipe and then system should say wiping rom. when done back out to main page.
6.click install, locate bb8 select then click back and select the gapps you downloaded
7. slide finger across to install both. ( if gapps fail don't worry back out (do not reboot) to install and select the gapps package again an install.
8. reboot and sign back into google. If you want some apps that are missing such as gmail or calender go
here download the apps you want and move them to system/apps using a file manager. then you have to change the permissions for them to work. If you don't now i will write it up for you.