This is one of the most powerful of the Protection Mantras.This mantra is used to protect one from potential danger and negative energies from all the 4 directions.
Whenever one feels he is in danger this Mantra should be chanted continuously.This mantra is said to protect one from negative energies including all sorts of evil spirits, enemies and danger from wild animals.
The procedure for acquiring Siddhi [mastery] is not there in this mantra. The only rule given is chanting it continuously when in danger.