Veeru,
you can find some good information about the FFT
here. If you need help with a specific analysis function of your development environment, please refer to the online help for this function for more information.
You have posted this question to the Motion Control board which doesn't seem to be a good fit for this type of question. Please post your questions to the appropriate boards (e. g.
LabVIEW,
LabWindows/CVI or
DIAdem).
Thanks and best regards,
Jochen Klier
National Instruments