Mr Kumar,

There is available a relative good explanation here:

https://www.chem.wisc.edu/~nbo5/ch3nh2.html

Thank you very much Bojidarka B. Ivanova.., i will check and respond to you very soon

Also, you can find some useful information here:

http://www.cup.uni-muenchen.de/ch/compchem/pop/nbo2.html

http://nbo6.chem.wisc.edu/tutorial.html