This guide is for version 1.2 of Creatures 3. If you do not have version 1.2, you can still get the patch, courtesy of Gameware.
Also, much of the information is relevant for the free Docking Station add-on, so it is also covered here. Be warned that much of the material is specific to Creatures 3, but there is much information that pertains to Docking Station.
Note: You can of course download lots of free (and buy some non-free) unofficial add-ons for Creatures 3 and Docking Station. This guide does not cover them.
Docking Station
Docking Station is an official, free online Creatures game which can optionally interface with Creatures 3. You can download it from Gameware.
Note: A section title with "(C3)" at the end pertains to Creatures 3, and a section title with "(DS)" pertains to Docking Station. If the section title has neither of these at the end, it's general information which can probably be applied no matter which game you're playing.