What is FFT analysis? how to analyze it?

The Fast Fourier Transform (FFT) resolves a time waveform into its sinusoidal components. The FFT takes a block of time-domain data and returns the frequency spectrum of the data. The FFT is a digital implementation of the Fourier transform. Thus, the FFT does not yield a continuous spectrum. Instead, the FFT returns a discrete spectrum, in which the frequency content of the waveform is resolved into a finite number of frequency lines, or bins

The formula is as Follows 

T is the acquisition time

N is the number of samples acquired

fs is the sampling frequency

Compute N with the following equation:

N = T · fs