Performance art is about two things:
The art of performance is the opposite to the art object and the idea of the "finished work"
Performance artists include:
It could be said that performance art is a rather recent phenomenon, beginning in the mid 60's around the time that gave us "happenings".
Essentially performance art is theatric, usually an embodiement of a theoretical and conceptual platform and frequently like a externalized condensate of accumulated experience/thought.
Performance art is not acting!
Performance artists work in the realm where their body and all it's capacities and limitations are the factors that determine the parameters of the performance.
Just like painters put their message on canvass and photographers make prints, performance artists make performances. These are not pre-rehearsed plays but rather more like experiments with the body and often without a known or even specifically desired outcome.
Above all, the body in performance confronts the public, the "witness". A great deal of performance art involves a physical discourse or comment about the the political and social behaviour witnessed in the daily life. We often experience performance art by immagining ourself in the role of the artist (s). While this is natural as a reaction, it's no more useful than painting immaginary brushstrokes or playing the immaginary musical instrument and we'd be better off discarding this replacement association and opening ourseves to the experience derived from reflecting the performance.
This is about all I can say about a subject that needs to be experienced. If you are still hungry for more info, do a websearch on the performance artists listed above or visit some of the pages below.