Hexadecimal numbers are used in MAC addresses (hardware addresses) in computers. This gives an unlimited number of possible combinations to computer manufacturers. That way each PC in the world has a unique identifier. Esuka Endeley Hexadecimal is a number system using Base 16. It uses the digits from 0 to 9 and the letters from A to F, A=10, B=11, C=12, D=13, E=14, F=15. It enables very large numbers to be written with fewer characters. As computers have very large memories, addressing specific parts of them becomes a big task. Hexadecimal is used as a way of doing so. Sometimes if your computer crashes you will see an error message showing a number with letters in it. Those letters are always between A and F. Basically what it is saying is that there was a problem in memory at this point.
Hexadecimal is used in many other ways in computers. One very common purpose is for colour codes in web pages. 6 digits are used, with 2 representing the amount of Red, 2 the amount of Green and 2 for the amount of blue. So if you want a lot of Red, but not much blue or green as a mix for your colour, the code could be something like FF0502. FF represents 255. If you do a web design course, specifically learning to use HTML for creating colours on your pages, you will learn more about this.