The chapter starts with a discussion of unit planning. It discusses identifying what you want them to know, the need to identify prerequisite knowledge, create a conceptual map to help organize the content, identify assessment methods, and decide what would be the next logical step for the students after completing the unit.
The next topic in the chapter is lesson planning. It starts by stating that lesson plans may have to be altered "on the fly" to take advantage of "teachable moments", and that teaching should be student centered not content centered. The chapter then goes on the discuss the components of a lesson plan:
The chapter illustrates being specific with lesson plans through an example of a poor lesson plan and a good one.
The chapter goes on to a discussion of "lesson imaging", where a more experienced teacher can do a "rough" lesson plan due to their prior experience teaching the topic. The last part of the chapter is a discussion of the importance of reflecting on a lesson after teaching it.
If you don't reflect on the lesson that you have taught, you won't learn anything from teaching it. If you don't learn from teaching, then you are going to wind up repeating the same mistakes over and over again, and you will never improve. By reflecting, you will have a better chance to identify new ways of doing things, and by writing down your reflections you are much more likely to remember what went wrong next time you teach the lesson (which could be a year later) so you won't repeat the same mistakes.