Images are represented with window width and window center values derived by DICOM tags or pixel values. Normally you can change interactively the windowing with right mouse button (if configured to act with this behaviour).
You can use Window/Level presets contained in a combo box and modified by INI file.
Reset button applies on the images the original values (and resets the orientation modifiers too).
Automatic Settings button applies a windowing derived by pixel values (such that the window is adaptive to the values).
The mouse sensibility combo box affect the way Windows/Level change during mouse movement.