How do I root my LG G4 Beat phone?
find a custom recovery for your device like TWRP or CWM then flash it or boot it in temp mode using commands like
fastboot flash recovery twrp.img or fastboot boot recovery cwm.img

then download su.zip from chainfire website and flash that zip vola your device is rooted 

you might have to oem unlock bootloader to do this

for that use command

fastboot oem unlock