Here's what the Harmonix user interface looks like...

The display can be split in the preview area (left side) and the configuration area (right side).

Preview area
As you can imagine the preview area shows a preview of the final image.
You can zoom in or out of the image by using the [+] and [-] buttons respectively.

Configuration area
In itself, the configuration area can be split into multiple areas; the two top-most sliders are known as the frequency controls.
The 20 sliders in the box beneath the frequency controls are the harmonics controls.
The slider at the bottom is called the wave control and all the buttons are the system controls.

Frequency controls
The frequency controls set the base frequency on which all harmonics will be based.
The frequency is measured in the number of full waves that will fit onto one screen. With the "fine%" slider you can add in part one whole extra wave to the total amount visible.

Harmonics controls
These controls appear in pairs of two where the leftmost of each pair controls the amplitude and the right one controls the phase (= horizontal offset) of each harmonic frequency.
The leftmost pair controls the first (or base) harmonic whilst the rightmost controls the tenth harmonic.
Each offset is scaled to the width of a wave of that harmonic frequency which means that shifting two of the offsets an equal amount will not shift the frequencies in an aligned manner.

Color controls
The two controls at the bottom left of the Configuration area let you specify the color of the wave.
Click on the color box to pop-up a standard Windows dialog which allows you to select a color or click the [F] button to use the current foreground color of your graphics application.

Wave control
This control simply sets the width of the line that represents the wave. This is also the only setting that is not automatically scaled to the image dimensions thus the preview will not give an adequate representation of this effect unless the zoom mode is set to 100%.

System controls
These buttons control the most basic of operations.
The [O] button allows you to open any previously saves settings.
The [S] button will allow you to save the current settings for later usage.
As to what [Exit] and [OK!] will do... well... you'll just have to find out for yourselves :)