An operating system or OS is a software program that enables the computer hardware to communicate and operate with the computer software. Without a computer operating system, a computer and software programs would be useless. The picture is an example of Microsoft Windows XP, a popular operating system and what the box may look like if you were to visit a local retail store to purchase it.
When computers were first introduced the user interacted with them using a command line interface, which required the user to perform a series of commands in order to interact with the computer and its hardware and software. Today, almost every computer is using a Graphical User Interface (GUI) operating system that is much easier to use and operate.