Segmenting is breaking a lesson in to more digestible chunks as to not over-burden to learning. Retraining is to reference and reteach ideas in previous lessons when when progressing to re-enforce the knowledge gained. Some material is just difficult to apply the follow coherence principle. In some cases that can take away from the purpose of the lesson.
There are many different ways to segment a lesson. Clark and Mayer suggest that adding a continue button on each segment allows people to work at there own pace. I would suggest a more economical way to achieve this would be to make the project a power point and have each slide
The GPC icollege instruction starts each section of by segmenting the whole tool into separate lessons. These segments are called the lesson objectives.
The pretraining principle is giving users basic information to work with before the actually start of the lesson. For example it could be a quick overview of the whole lesson before the breakdown into smaller segments. When explaining complex process it often helpful to have foresight on the outcome.
In the GPC iCollege documents, Each lesson also come with and overview, this will introduce any new language and terms that the user needs to understand to become familiar with the section.
e-Learning and the Science of Instruction; Ruth Colvin Clark • Richard E. Mayer