Spectral analysis using pwelch

How can I extract the first 2 seconds of data from a 1 minute .wav file and then asked to fragment it into 200 segment of 10 ms of each? Then I have to estimate psd using the pwelch function and store the result as matrix, and plot the spectrogram using the imagesc.

[Waleed ElGrawani]

why dont u use spectrogram function with 2 seconds window