Applications :: How Itunes Imports Existing Files

I'm trying to understand how itunes imports files and where it puts them. Does itunes duplicate existing files when your first install it?

In other words if I have some songs and videos in my computer and I install itunes, I know it will search for files during the installation and add them to the itunes library so, here is where my question comes, does itunes copies the files it finds to the itunes library and leave the exiting files in its original location or it moves them to a new location?

I'm just trying to understand how itunes imports and stores files and where it puts them.