This is a good question.

There are many books illustrating the FFT.   To get started, see

https://www.researchgate.net/publication/290440858_The_Fourier_Transform_in_a_Nutshell

https://www.researchgate.net/publication/293140288_Fourier_Transformation_for_Pedestrians

https://www.researchgate.net/publication/311420765_Vibration_Analysis_and_Diagnostic_Guide

See, also:

https://www.researchgate.net/publication/229009548_Scalar_hysteresis_measurement_using_FFT/figures?lo=1

Article Scalar hysteresis measurement using FFT

Article Convexity and the difference property

Chapter The Fourier Transform in a Nutshell

Book Fourier Transformation for Pedestrians

Book Vibration Analysis and Diagnostic Guide

Thank you very very very much sir!

Oppenheim's book, "Discrete-Time Signal Processing," provides a detail example of 8-point FFT in Chapter 9.  The foundation of FFT, which is DFT, is introduced in Chapter 8.

Thanks sir.

Theory and Application of Digital Signal Processing F First Edition Edition

by Lawrence R. Rabiner and Bernard Gold.

Thanks

The best book I found on the subject is still "The Fast Fourier Transform and Its Applications", by E. Oran Brigham

Thank you sir.

For quick knowledge about the topic I recommend: "A first Course on Wavelets" (Guido Weiss and Eugenio Hernandez, CRC Press (2000)) in Chapter 9.