You can't flood fill in DIS and you can't save "patterns" as in PS. If you have an image of glitter, you can go to Effects/Fill with texture or color/Picture. If the picture you want to use is already open just double click on it from the right hand side. If the pic you want to use isn't already open just click on "open a picture" and browse to where it is saved.
As for gif animations: In DIS, you can't use a pre-animated image and keep the animation. Once you alter it, it will no longer be animated. There is a solution though. If you break down the animated gif into "layers" you can then open each layer in DIS, add any other pics or text and then use Flipbook to make the new animation.
To break down the animated gif go to
http://www.gifworks.com/image_editor.html and follow the instructions there.