Ok, so we know how to add. Piece of cake. As it turns out, Multiplication is already pretty much within our reach.
If I were to describe it very briefly- I would tell you that you've already figured out the crux of it. Multiplication is really just a repeated series of additions, and I urge you to keep that idea at the forefront of your thoughts as you read chapter 4.
However, I have to add here that this textbook becomes a lot less the "comprehensive end-all guide" and more of a book fine-tuned for the needs of CMSC389E here. That is, we do take some liberties in simplifying the problem of Multiplication in digital logic circuits, and make it easiest to understand in the context of this class. If you want to learn more about different multipliers and their nuances, please feel free to delve into an engineering department digital logic class.