url - you can specify any url that points to an image resource in the web. The url must be the exact location of the image - e.g. http://some-site.com/image.jpg .
upload - you can upload image from your computer - the uploaded image is available only for the game-play. If you want to make another game with the same image you have to upload it again.
How to play?
Simply choose the image and select the number of pieces that the puzzle will contain. After that you can select and move the pieces with the mouse.