Take a look at this for illustration of the mechanics of how the function works:
x = exprnd(2,20,1);
The plot on the left is the probability plot. The plot on the right is the same plot, but with all the special "probplot" stuff removed.
So by looking at the plot on the right, you can see it's your sorted data plotted against quantiles from a standard normal distribution. However, on the left you can see that the y axis scale has been changed to correspond to probability values from the normal distribution. Data from a non-standard normal distribution (other than mean 0, standard deviation 1) would have the same shape but the intercept and slope of the line would be different.
For some distributions like the Weibull one you showed, the x axis has a log scale. This is so different parameters would change only the intercept and slope.
Daniel gave a good answer related to the interpretation of the plot.