This was one of the best explanations of the tool in ART that I recall and should help to answer that one
As for contrast with the other tools really each might be at a slightly different spot in the pipeline and so alter contrast a bit differently but really they are all just about making bright things brighter and dark things darker and in some cases you can select the pivot point for this ie what is dark and what is light and then its a matter of how steep you make itā¦steeper is going to be introducing more contrastā¦ with the curves you can also introduce a transition to white and blackā¦