What is a base 16 numbering system

It is called Hexadecimal, and consists of the numbers 0-9 followed by the letters A-F.

A=10 B=11 C=12 D=13 E=14 and F=15

Data is stored on computer in Binary Digits (BITS) which count up in 0 and 1
and can be grouped into 4 bits (BYTE) so the full hexadecimal table is as follows:-

Hex Binary
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
A 1010
B 1011
C 1100
D 1101
E 1110
F 1111