Java Shmava

Why is java on my computer Why are the updates larger than the original and why so many of them.. Do I really need it and why. I called sun and all they could tell me is that its for writing programs which I would'nt have a clue how to do..A few more updates and it will be larger than my operating system. You say its been around for a while and everybody should know what it is but I have asked numerous people and none of them could explain what it is. Certainly your explaination was all greek to me.. All I need to know is do I need it to use my computer...