A: N-Score and probability are the same.  The n scores are the z scores from a standard normal distribution ie. mean 0 and sd 1 (hence n score, not z score).  Data is plotted against the n scores from that distribution.  If you picture the bell curve, these are the numbers on the x axis in units of sd.  If you replaced these by the area under the standard normal curve they would be probabilities, so, an n score of 0 (middle) would have an area to the left of 0.5 so a probability of 0.5.  An n score of 3 would have a probability of 0.99 or so.  To view Probability values on the X axis click on the Change X ticks button on the RHS toolbar.