A computer is a machine that performs tasks and calculations based off a set of instructions, or program operations.
Electronic computers were introduced in the 1940s and they were huge machines that actually required a team of individuals to operate.
In contrast to early computer systems, today's computers are vastly smaller and amazingly powerful. Not only are they thousands of times faster but they are small enough to fit on your desk, on your lap, or even in a pocket.
In a nutshell computers work through an interaction of physical hardware components and software instructions. Hardware is the actual physical parts of a computer that you can see with your eyes or touch with your hands.
Software is basically a collection of code that makes up a computer program. The hardware in turn carries out instructions by a computer program on a complex level using electricity.
When talking about computers the most important piece of hardware is a chip inside your computer called the central processing unit, or in short a CPU. Microprocessor is also a very common term used. Think of it as the "brain" of your computer. Like your own brain it can translate instructions and perform calculations.
Other hardware items such as a monitor, keyboard, mouse, printer, video card, sound card, or other physical piece are often called hardware devices or even just devices for short.
When looking at software, it is the actual instructions, or programs, that tell the hardware components what to do. Without software the hardware is essentially useless. A computer game, word processing program, or Internet browser are some common types of computer software.
Of course the most important piece of software for a computer system is the operating system or also commonly called just the OS for short. It is responsible for managing your entire computer and all the devices connected to it. Popular operating systems include Windows XP, Windows Vista, Mac OSX, and Linux among others.