how to show frequency domain?

hi, i'm begginer in matlab and i have question how to show the frequency domain for this code:

t = linspace(-2*pi,2*pi,200);
sinyal = sin(t); %Sinyal Asli
sigma = 0.07; %Standar Deviasi Noise
sinyaln = sinyal + sigma*randn(size(signal)); %Sinyal + Noise
subplot(211)
plot(t,sinyal); axis([-8 8 -2 2]);
title('Sinyal Asli')
subplot(212)
plot(t,sinyaln); axis([-8 8 -2 2]);
title('Sinyal + Noise')

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/matlab/examples/fft-for-spectral-analysis.html

[raizal muttaqin]

please give me more detail about what should i do to my code. thanks...

[Walter Roberson]

You follow the example there, but substituting your own data.