honestly, I have no idea what it is. I have it standing on my pc but I never clicked on it? can anybody tell me what it is please.

It's the main program that mods are built with.
It's what Bethesda used to build the world of Morrowind.

For info on what you can and cannot do with the CS, check http://www.gamesas.com/index.php?/topic/1295545-a-question/page__view__findpost__p__19517501