Advanced transformations use mathematical transformations to skew, slant, twist, slice and dice your images. The built-in transformations are accessible in the Effects->Transformations tab of the main menu.
To apply a transformation effect to the whole or a part of an image, choose the transformation name from the menu and click on it. You will see a dialog window with the effect formula, argument values and the preview screen. Slide the argument value bars to the left and to the right and preview the changes in the adjoining preview window. When you are happy with the effect's result, click "OK" and you will return to the main screen.
You can also create your own advanced transformations.
Note that advanced transformations apply to selected regions. By default the whole image is selected. When you select an area of the image, the tools apply changes to the selected area only.