Fourier transform to MATLAB

Please tell me about the Fourier transform in the MATLAB environment. The 3rd day I try to understand through Google and periodic logs... There is a set of EEG signals: 500 values in 2 seconds (frequency 250 Hz). I just need to decompose them into a spectrum (as far as I understand from 0 to 125) and get the values of 2 bands: from 0.5 to 14 Hz and from 14 to 40 Hz. But even the decomposition into a spectrum, I believe with an error:

% init
fs = 250;

% load
da = da1_all;
x = da(1:256,1);

% Построение графика спектральной плотности
fx = fft(x);
sfx = fftshift(fx);
f = linspace(-fs/2,fs/2,length(x));
area(f,abs(sfx));
title('Амплитудный спектр сигнала');
xlabel('Частота(Гц)');
ylabel('Амплитуда');