The gHowl download includes several example files. Let me know if you have any other questions after running those. The video you link to shows a custom interface inside of gh/rhino. While gHowl could provide something like this by combining it with processing or another external application (Processing, vvvv) or device (TouchOSC/MRMR on iPod/Android), it does not provide an interface builder inside of Rhino. gHowl was created to communicate with applications and devices outside of Grasshopper and Rhono. With some time, what you want is not too difficult to construct in a vb or c# component. Check out this interface written in a vb.net component.