Here is my first "real" quartz composer prototype. I duplicated the spirit of our kids' photo app 'dipityPix. This means 4 moving sprites that randomly adjusts posterization thresholds when hit with a mouse.
First I use an interaction routine for each sprite that logs mouse events. These are only live if there is a link between the interaction routine and the sprite (which is just a connection you make with the mouse). The sprite has one of two images depending on whether the mouse is pressed. Again this is just making the appropriate links.
Second we need random numbers. The Random routine just spews a stream of random numbers and we only want when when the mouse is pressed for that ball. Thus we "sample and hold" it when the number of mouse click changes (very basic dataflow concept and surprisingly hard for me to get used to because state is more "in your face" in C-like languages).
And that's it. I can see why people love the environment for prototyping.
For learning these basics the best resource I found was this excellent series of youtube videos by Rob Duarte. And here is the code for the example above.