An extension is how the new url will end. Some websites out there will not let you post an image onto their site with the image tag, unless it has a valid image extension. So if you're expirencing problems like that, you can put your url to the image in the box, and then pic out the extension you would like!
Will you ever delete my url?
Currently, no. But if I see the url hasnt been reached, visited, or used in about 6 months, I will delete it. So if you're url is in use you will have nothing to worry about
I have an image that I made the url short to, and I would like to change that image.. How do I do this?
easy! Just change the file names on your hosting site for the image, and make the new image you would like the same file name.