VomitHatSteve's video shows the basics...just point your camera into a monitor showing the camera output and go from there.
A couple of hints...
First, for the completely abstract view you want, zoom in so you don't get the edges of the monitor or any screen display captions in frame.
Once you've done that, introducing even a minor tilt will start things going funny, as will gradual zooms in and out and racking in and out of focus.
As the video shows, putting any kind of object, preferably coloured, briefly in frame can set things off nicely.
Once you have things moving with some combination of tilt, zoom and object the feedback will tend to keep going by itself but you can trigger changes by changing one of the settings.
Video feedback is fun!