How to smooth a periodogram with Pwelch.m?

Hello everyone,

I am trying to smooth a periodogram obtained by FFT.m with Pwelch.m . I studied the materials on Matlab Help, but I don't know where to start and how to do it?

Here is the code for FFT:

loglog(omega,Pu(1:round(N/2)-1));

this gives the periodogram from FFT. Now I am trying to use pwelch on Pu.Is there anyone who can help me?

Regards,