A.2 - A brief discussion of gates, truth tables, and logic elements. You'll need to understand this material to to Assignment 1.
A.3 - Decoders and Multiplexors, as well as two-level logic and sum of products, as well as Don't Cares and Arrays of Logic elements. We don't care about PLAs, but the ROM material is also of interest. And Multiplexors are the most important element from the digital design portion of the course for CS 251.
Be sure also to look at exercises A.1 and A.2 on page A-79, which talk about DeMorgan's law.
The Circuit examples videos shows how we use this material.