University of California, Santa Barbara: Behrooz Parhami's "Part I: Number Representation"
Read through slide 37. These slides explain how numbers are represented, i.e., encoded by using a string of bits - or binary digits. These lecture notes also describe how the sign of a number is represented and how 2's complement representation. Finally, skim slides 38-88 to get a basic understanding of what they cover: redundant number systems and residue number systems. This material may or may not be difficult, depending on your mathematical background; make sure to take your time as you study this material.