Hex is used in mathematics and information technologies as a more friendly way to represent binary numbers.
The letters are used because of the need to represent the values 10, 11, 12, 13, 14 and 15 each in one single symbol. These are the 10 decimal digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) and the first six letters of the English alphabet (A, B, C, D, E, F). As a base-16 numeral system, it uses 16 symbols. The hexadecimal system (shortly hex), uses the number 16 as its base (radix).
It uses the number 10 as its base (radix). The decimal numeral system is the most commonly used and the standard system in daily life.