What is political and economic transformation of Western Europe after the fall of Rome?How did the organization of Medieval European societies...

This is a pretty big question, and the answer is not the same for every time and place after the fall of Rome.  But in general, the ideas of decentralization and self sufficiency go a long way to describing what happened.

After the fall of Rome, Europe split up into all sorts of little political entities.  Where Rome had once ruled a large part of Europe, it now came to be ruled by "nobles" who controlled as much land as they could.

Self-sufficiency became more important after the fall of Rome.  Now that Rome did not control everything, it became very dangerous to travel and, therefore, to trade.  There were too many people who might steal a trader's goods and money.  So there came to be much less trade and areas needed to be self-sufficient.