don't really understand your question, but I guess you want to to know what functions are being used above:
fittype: Fit type for curve and surface fitting
fit: Fit curve or surface to data
What you are doing is trying to get the fittype for your data based on the expression 1-exp(-a*x^b) and then using that fittype which you have in 'h' now to fit a curve to your data using
[Y,par]=fit(r',P',h,'StartPoint',[1 1]);