Properly interpreting FFT output

1. What does the output of FFT mean?
2. What does an FFT plot tell us?

What does the output of FFT mean?

These frequencies actually represent the frequencies of the two sine waves which generated the signal. The output of the Fourier transform is nothing more than a frequency domain view of the original time domain signal. For more information and background on the Fourier transform, take a look at this link.

What does an FFT plot tell us?

Frequency-domain graphs– also called spectrum plots and Fast Fourier transform graphs (FFT graphs for short)- show which frequencies are present in a vibration during a certain period of time.