You can create your own macros using the menu option "Macro=>Edit/Create". For an introductory tutorial on how to create your own macros see this link.
The GSAK macro editor is a light weight editor that will allow you to add and change GSAK macro files. Macro files should be created with the extension of .gsk to be compatible with the macro manager.
However, as GSAK macro files are just plain ascii text files you can use your favorite text editor (even notepad) to edit these files. The GSAK macro editor is provided as a quick any easy method to access macro files, but I suggest you use a different editor if you want more sophisticated features. GSAK allows you to configure your own programming editor to replace the GSAK macro editor.