Value in art is essentially how light or dark something is on a scale of white to black (with white being the highest value and black being the lowest value). It is widely considered to be one of the most important variables to the success of a painting, even more so than your selection of color (hue).
It has lots of shades that can tell you exactly what and where this woman is. The shades tell you that its night and there's a wine bottle so maybe the woman just got out of a relationship or had a bad day.
