Shaman:

A shaman is a community healer. A shaman is in service to those whose lives she shares. A shaman accesses altered states of consciousness, perhaps with the aid of psycho-active plants, or a repetitive drum beat, or with chant, with prayer, with physical extremes.

She is at once a vital part of her community, and a person who is outside the norms of her community. She is often chosen and trained from birth, or she makes herself known by certain experiences that befall her around puberty. (For instance, at the onset of my puberty,

I was stricken with viral pneumonia, and was nursed, at home, by my mother, for the two months I lay in a feverish hallucination. The last thing I remember is reaching behind myself to tie the bow on my dress; the next thing I remember is two months later, my mother spooning baby food into my mouth.) A Shaman is the representative of the Life Force..

Priestess:

A priestess serves the holy space for the community. She tends it, guards it, beautifies it, maintains it, repairs it. She is in service to the ritual and the ritual objects. Statues are dressed and undressed, washed, moved, displayed, paraded. Icons are lit, washed, filled, emptied, dusted, polished. Flowers and incense, water and fire, the priestess is responsible for the elements within the temple. She brings music and song to the ceremony. 

A priestess can have real power, or she can be "just for show." It may be hard to tell the difference, for there is a lot of show even in real power. Look for her athame (her magical knife) or her staff of power. (And do be careful not to touch her ritual tools.) Ask who initiated her. Be aware of how she directs the energy of the ceremony. The Priestess, especially the High Priestess, is the one who gives the ritual its presence. She creates a clear beginning, middle, and end and a specific focus for each sacred ceremony.

Once you become sensitive, you can feel the power that comes when a woman sets aside her personal ego and takes responsibility for the good of all.  A Priestess is the representative of the Goddess.

Witch:

A witch is a woman whose life is her Art.

A witch works magic.

A witch creates spells.

A witch makes potions. 

A witch has a familiar.

A witch can be solitary, but she is always sought out.

A witch can be a grandmother; yet witches are known to eat children.

(A book of Inuit stories that I read one winter told tale after tale of grandmother secretly cooking the children for supper when father came home empty-handed from the hunt and blizzard winds blew.)

A witch is the representative of the Earth.