Computers and brains have much in common, but they're essentially very different. What happens if you combine the best of both worlds—the power of a computer and the amazing flexibility of a brain? You get a superbly useful neural network.

Artificial neural networks have made computer systems more useful by making them more human.

http://www.explainthatstuff.com/introduction-to-neural-networks.html

P.S.: I'm not researching in any of these fields personally but I know they have the same research standard than the rest of the image processing and understanding community.

Thank you Mr. Martin...

Basicaly to get general idea how it works is not that hard and one can say it is easy (specialy if one has really good imagination which helps). To completely understand each parameter which can be tuned and to be able to properly train usable model can be hard. To come up with some new idea it can be really hard. So as Bruno Martin said, it really depends on what paper exactly is saying.

Neural Net calculation is basically a formula-based calculation, so when compared to AI, the Neural Net is relatively much easier than AI.

Because the AI system should generally have a mechanism

rule-based processing and mechanisms for explaining the reason for selection of rules

Thank you Sir.