The existing images tab allows you to view any images that you have uploaded to the site (you can only upload images with a .gif, .jpg or .png extension). You can then copy the full path and use it in any pages you create to show an image. You don't have to use this feature, and if you have any images stored elsewhere on the internet, you can still just use the path to those images.

You can also delete them by clicking the delete button.