The settings dialog consists of four notebook pages: Document, Layout, Ghostscript and Printing.
In the Document page, you can set the fallback media type which is used if the document does not specify the media type. If "Override document media" is selected, the fallback media type will be used regardless of whether the PostScript document specified its own media type. Fallback media type should be set to a common paper format (like A4 or Letter) that is probably used by most PostScript documents you will display. The "Antialiasing" setting tells Ghostscript whether to use anti-aliasing when rendering data (ie x11alpha device as opposed to x11). Antialiasing improves dramatically the quality of the displayed documents.
The Layout page lets you choose whether GGv should show the toolbar and the menubar by default. Both menubar and toolbar can also be hidden on a per-window basis by using the menus or the pop-up menu.
You can specify the commands that GGv uses to call Ghostscript interpreter in the Ghostscript page. The "Interpreter" should contain the full path of the Ghostscript executable with any strange options you might desire, "Scan PDF" should be the full path of the Ghostscript executable with the options used to scan PDF files and finally, "Uncompress" should be the command used to uncompress gzipped PostScript files. You should leave these untouched unless you know what you are doing.
On the Printing page, you can specify the command used to print the document. The filename passed to the command should be marked with %s.