ॐ उग्रं वीरं महाविष्णुं ज्वलन्तं सर्वतोमुखम् । नृसिंहं भीषणं भद्रं मृत्युमृत्युं नमाम्यहम् ॥
You cannot understand Narasimha Vidya without understanding the Puranic event that gave it birth.
The most potent form of Narasimha Vidya is the or the Panchamukha Narasimha Mantra (five-faced).
If you are not initiated, do not use the Beeja mantra. Use the full "Ugram Viram" verse. Here is a 10-minute daily practice:
The Radiant Path of Narasimha Vidya: Wisdom, Protection, and Self-Realization