Hmm, not exactly. The Wikipedia article actually sums up the most important mechanics nicely enough. Basically, in a contest, a player rolls for his/her character and I roll for the opposition. The rolls are then compared, determining the level of success/failure, which then determines how the outcome is narrated (among other things). Critical outcomes can bear pleasant/unpleasant surprises, as can minor victories or defeats, while more moderate levels of success are more in line with what might have been expected to begin with.