We are going to merge the blur graphic with the original, otherwise all that shows up is the blurred copy. We use the merge and mergenode elements. Not much to explain here. It just merges what you type in into one image. Now all you need to do is apply the filter to your graphic.
Lets use a text area.
There you have it, your first filter. Not hard at all. We will go into some more advanced stuff later. But I think this will give you a good start on experimenting with your own filters. Keep checking the filter section for new filter examples.