FFT output spectrum generation

Hi all,

I just have a simple question regarding to FFT output. I understand that the output of the real and imag signal have signed value, and these has to be divided by exponent value in order to get the real value. The question I have is how should I get the spectrum more specifically range and the magnitude of the specific frequency! I am new to FFT core. I am looking forward to your reply! Thank you very much!

Best,