How to create an AppImages from deb or tar.gz?

I have a software downloaded from web in deb and tar.gz files which I have not installed in my system itself. I want to convert these files as an AppImage for personal use. How can I do this?

In the web I have come across pkg2appimage which says

If you already have existing binaries (either in archive or .deb format or a ppa) then the recommended way to convert these to an AppImage is to write a .yml description file and run it with pkg2appimage:

There is also a list of examples for yml files but I really don't understand how to write yml files for appimages.