What makes a Posek a Posek?

I was wondering what exactly makes a Posek a Posek and how does the Halachic methodology work?

Kol Tov!

A posek is someone who is learned in Shas and Poskim AND has a mesorah of how to pasken halacha that was taught and passed down to him by another posek.

Regarding Halachic Methodology, that is a complicated one and varies based on region and Rav and would be difficult to explain on a forum such as ours.