Ygritte is a wildling (or "the free folk," as they tend to refer to themselves) living in the lands beyond the wall. Ygritte is used to a life and worldview based on old ways, old mysticisms, and the old gods of the north. She and her brethren do not understand the minds of those who kneel to a king - nor does she have any love for "crows," the black brothers of the Night's Watch who guard the wall.
Jon Snow and his brothers will find in Ygritte a level of beauty, passion, fierceness and cunning they didn't expect in the so-called "wildlings" beyond the wall.