I'm not certain that I've figured this one out correctly but it should return the value of a (Gaussian) normal distribution of the given properties at the given location.
$x - the X-Value to request
$ave - the 'expected value' (i.e. location of the peak) for the distribution. For most uses this will just be 0.
$stdev - the standard deviation of the distribution. For most uses this will be 1.