How do I unlock bootloader and root LG Optimus Zone 3 (VS425PP)? How do I unlock the bootloader on LG Optimus Zone 3 (VS425PP) in a simple, easy to follow steps?

Then how do I root the device and return to a fully functional cell phone that is stable and rooted? Can't get any help from using FlashFire, KingoRoot, SuperSU.
You cannot unlock the bootloader on the LG Optimus Zone 3.

However, you can root the device using a system-wide root strategy -- thus avoiding the inevitable risk of modifying the boot image, KingoRoot is the best method -- however, you must be running an older firmware build such as vs425pp2.

To downgrade to vs425pp2, you will need a KDZ or TOT firmware package and LGUP Dev Edition. 

Once the root is established, you may use SuperSU-Me Pro to substitute the KingoRoot binaries with SuperSU root binaries. Then you can use FlashFire to upgrade back to a more recent firmware build, maintaining root with the EverRoot feature.