use chainfire (cf-root) method - very reliable and by far the most favoured method on here.
the kernel is part of the firmware. you will have a stock KI8 on your phone now.
to root you would need chainfires insecure kernel to replace the stock kernel, you just find his KI8 file and flash this, it will replace your stock one.
you are then rooted.
you would then be able to change to different custom kernels if you wished eg. siyah, speedmod, ninphetamine etc etc. these have different featrues/tweaks to try and make your phone perform better, or the battery last longer, or add features such as BLN (back light notification). it does no harm trying a few to see what suits you