The scale editor is where you can create and edit the scale being used. For each note in the scale there is a row of controls in the bottom part of the window, plus a row at the end which represents the first note of the next octave.
Notes can be added or removed by editing the 'Number of Notes' field.
Pressing the equal temperament button changes the notes so that they all have an equal interval.
For each note in the scale you can set it's pitch either as a ratio or as a value in cents.