The geoCable is a custom cable that interfaces the user port on the Commodore 64 to the parallel port on a printer.  I found this short article on how to make the cable HERE. Thank you Internet Archive for preserving this!  

Further information on this topic can be found HERE , HERE , HERE and HERE.  I've never built one of these cables, so I recommend cross referencing all the information until you're comfortable with your chosen solution.

Also, issue 72 of geoNews (August 1997) has a short article on page 3 about creating this cable.  

One last source for info on the geoCable - the CMB FAQ v3.1 - http://www.faqs.org/faqs/commodore/main-faq/part7/

geoFont Catalog is a listing of almost all the fonts available for GEOS printed in the actual font of each respective type.  This is a worthy document to have printed and near at hand if you do much with GEOS.  The document originates from https://www.lyonlabs.org/commodore/onrequest/geos/geoFont.pdf

This PDF is an excellent tutorial on how to use geoPublish. The tutorial is very thorough and full of great hints and tips. The zip file contains the 110 page Tutorial PDF along with the screen shots shown, 2*.d81 images and an FD-2000 .d2m image containing all the files that make up the tutorial plus a number of useful utilities for anyone using geoPublish.

enGEOy!

Laser Direct offered Laser Printing services for C-64/128, Amiga, Apple II, MacIntosh, and IBM compatibles in the late 1980's to early 1990's. 

The Publisher's Kit and the Laser Printers' Informational Kit contained in this zip file hold 49 pages of very useful info on how laser printers work, laser fonts, scaling graphics and especially a lot on using GEOS and geoPublish with a laser printer.

Both of these doucments will greatly assist a user trying to get the most out of geoPublish.

enGEOy!

Some good programming information for the GEOS desktop replacement called Wheels.