When you start up the PC Editor the first editing screen allows you to apply edits to the overall voice and are no different from those you can achieve in the onboard editor (Voice Set).
The main advantage of the PC Editor is that it allows you to modify properties of waveforms making up the individual voice elements in more fundamental ways. You need to click on each element (EL1,EL2 etc showing in that first window)
and then for each click on the blue Detail button that is present on the resulting window that appears.
That way you get a window for each element with a series of tabs across the top where you can select Oscillator/LFO/Filter Envelope Generator/Amplitude Envelope Generator etc.

Additionally you can add (or subtract) elements to a voice by importing selected/edited ones from other onboard voices or using wav. files where desired to "improve" the tone, or perhaps add new tones which come in at predetermined velocity ranges - such as turning smooth brass into trumpet stabs on demand for BigBand left voices for instance.

John