Some Spectrum terms&concepts

DFT: http://mathworld.wolfram.com/DiscreteFourierTransform.html

Leakage: http://mathworld.wolfram.com/Leakage.html

Aliasing: http://mathworld.wolfram.com/Aliasing.html

DC component :Corresponding to zero frequency. And this equal to sum of input array values. 

Fs ile Fi un tam kat olması : Apodization function: http://mathworld.wolfram.com/ApodizationFunction.html

* For real inputs real part of DFT is symmetric about Nyquist point and Imaginary part is anti-symmetric about Nyquist point.