The purpose for and use of this separate sheet of paper during the course of constructing entries when composing an organ fugue
using a computerized music writing application is fully explained on the Blog/Archive page. It will make more sense and be found very helpful by going there.
Sinply click the Blog/Archive page in the top menu bar, scroll
to the very bottom of the screen, click Overview, then scroll far down the right hand column to Feb 21 2017 to find and click the Ten Steps entry posted on that date.
One might then scroll down to Step Five which discusses the use of this sheet of paper and where it feeds into the entire process of steps.
Would-be fugue-writers will find these Ten Steps of
significant assistance in organizing the construction of a new work employing fugue procedure.