Well, the differential linegrowth etc is well documented here:http://forums.odforce.net/topic/25534-differential-curve-growth/#comment-148345
Entagma also has Tutorials on it.
The “shortest path” structures I mostly translated from my work in Grasshopper.
I can give you a quick intro - the basics are very simple: You define a couple of start- and end-points on any kind of grid/mesh (as groups) and the algorithm then finds the shortest paths between them on the grid and returns those paths as polylines. This gives you the basic structure if you for instance define one start point on the edge of a circle and all other edge-points as endpoints. From there it's massaging the starting grid itself and the parameters of the shortest path node to get interesting forms. Sometimes I also convert to NURBS curves afterwards for smoother lines.
The main problem is, that you get tons of overlapping lines which Mantra does not like at all… ;-)