The chapter from Taylor is listed as Essential for both Module 2 and Module 3. Suggestion: watch the Module 2 videos, read this chapter through once, watch the Module 3 videos, then come back to the chapter.
Reading
Taylor – Chapter 16 – Unit-selection synthesis
A substantial chapter covering target cost, join cost and search.
Jurafsky & Martin – Section 8.5 – Unit Selection (Waveform) Synthesis
A brief explanation. Worth reading before tackling the more substantial chapter in Taylor (Speech Synthesis course only).