Easy one this,
An Operating system is a program that controls the manner in which your Computer interacts with you,
among other things ;)
Some Operating systems are controlling and manipulative whilst others are free and open.
Most newer operating systems eg. Linux and Windows looks almost identical.
For some differences between Linux and Windows for example please see http://www.cutthecrap.co.za
Mostly you are the user and therefore must select an operating system best
suited to your needs. As I am biased on this matter it is impossible for me to
give you impartial advice

LINUX Rulez !!!