In a nutshell, a needlepoint Stitch Guide is a road map for stitching a design.
Stitch Guides are similar to "how-to" instructions, and will guide you through all of the steps and stitches recommended for completing a project - whether it is from a kit, painted canvas or pattern.
Stitch guides contain detailed information on how to work a particular stitch, and how to fit it to the area it is being used in. A good stitch guide gives as much information as possible, and is written in such a way that the person working the design can fully understand - and follow.
The Coins in the Fountain Cyberclass can be classified as a stitch guide - instructions are given in a step-by-step fashion, including specific information for working each section or stitch.
Use the Stitch Guide as a tool to help you work the design, step by step, stitch by stitch.
Stitch guides are often written by the original designer, but can also be written by a others who have worked the design, or by people who specialize in how-to or stitch guide writing.
But I do have some words of warning: Some stitch guides are very good - but some out there can be pretty bad, especially if they have been written by someone who has not actually stitched - and therefore experienced - the design firsthand.