What is level graph and Blocking flow in Dinic's maxflow algorithm?

I am learning Dinic algorithm from max-flow here.I am not able to understand the terms Level graph and blocking flow any one help me.

level graph means u r simply making a rooted tree where every node is at a shortest distance from root.
also the sink is at a shortest possible level from the src.

blocking flow means after u convert the residual graph into a level graph u pass maximum flow through the level graph and when it becomes impossible to send any flow further for the current level graph.

then again u make another possible level graph

i learned it recently and solved few problem with it.


provide the link to problems and some good resources to learn it.