Understanding normal distribution graphs

[DrVanNostrin]

I'm not sure exactly what you're talking about, but I'll take a stab. You were probably looking at a normal(0,1) distibution. This a normal distribution with a mean of 0 and SD of 1. If this is the case the x-values do correspond to z-scores. The y-values are a little more complicated.

Since a normal distribution is continous the probability of getting any exact value is 0 (there are an infinite amount of possible outcomes). However the area under the curve is equal to the probability of falling in that region. For example, the region bounded by x = -1, x = 1, y=0 and the distribution itself would have an area of 0.68. If you were to integrate from x = -1 to x = 1 the result would be 0.68 (you can't integrate a normal distribution using standard techniques). For any continous distribution the integral from -infinity to infinity must equal 1.