The Background course is advanced material and takes a deep-dive approach to subjects such as: delegates, generators, and extension methods. On the other hand, this background chapter is intended for beginners. It is for those students who have little or no knowledge of lambda expressions, generics, etc.
A very basic understanding of these concepts is pretty much required to effectively use LINQ. If you already are familiar with this material or you have already taken the Background Topics course, you can probably skim through or even skip this chapter.