What is the Featured Image area for on TwentyTen?

I am creating a child theme using the TwentyTen theme as a parent. I saw under the Pages area in the admin section, there is a ‘Featured Image’ area, but I don’t see where that featured image is shown on the page.

What is the featured image area for? I would ideally like to use that uploader to put an image at a specified location on the page.

In what file for twentyten can I find the code php code for the Featured Image area that is displayed in the pages admin area? I looked all through the functions.php file. I’m guessing it is a function in the core files and it is being called in the functions.php file in the twentyten theme, but I can’t seem to see where that is happening. Can someone help me?