The 'debian' directory contains debian source code for bionic, buster and later distributions as it uses functions only available with debhelper11+. 'debian_dh9' is used for xenial, stretch and earlier distributions using debhelper9.
When complete the produced debian packages will be located in deb_files_generated directory.
Arguments for the deb-buildsource.sh script that can be passed are either 'None' or '"your custom comments"'. 'None' assumes a permanent changelog entry has been made listing the correct build for the version. If you quote and enter your own comment string, it will be appended to the changelog for that deb package. If no argument is passed a default comment is generated saying that this deb package was generated by this script.