See Section 1.1 of The Most Complex Machine . Usually, you want to use both positive and negative numbers. The scheme for representing negative numbers is a bit strange. It is explained in Subsection 2.2.3 of the text. Using 32 bits, the integers from -2147483648 to 2147483647 can be represented.
Hexadecimal numbers are a kind of shorthand for writing such strings.
Each hexadecimal digit stands for four bits. A hexadecimal number is really just a number written in the base sixteen, just as ordinary integers are in the base ten and binary numbers are in the base two. You should be able to translate between hexadecimal and binary by hand. Real Number Real numbers are numbers that can contain decimal points, like 3.14159 or -234.5, or 12.0. The representation used in computers for real numbers is very complicated.