Firstly, you will have to choose the images that you want to include in the animations and define how long you want the interval time between the transitions. Creating the animation effect is then just a case of clicking the animate button so you can preview what you've created. If you the images in sequence, you should have yourself a pretty impressive Java animation.
The page generated with the animation also contains a small control panel that enables you to slow down and change the intervals. A useful little program that makes java animations easy but would have been a lot more useful if it included options to create other Java functions.