This kind of fitting allows to fit your data points to a sum of Gaussian, Lorentzian or Pseudo-Voigt functions.
The first step is to specify the number of peaks. Then you must define the position of each peak on the curve. This is done by clicking on the plot, then validate your choice for each peak with the ENTER key.
When the selection step ends QtiPlot pops-up a dialog that summarizes the positions of the peaks and lets you choose if you perform the fit using these parameters or if you want to open the Fit Wizard and refine the initial guesses before performing the fit.