Problem in getting Power Spectral Density using frequency analysis

I am currently working on my final year project and my topic is "Structural Health Monitoring"

I am supposed to get Power Spectral Densities of the given frequencies. For that, I need to detrend given data, apply a Butterworth low pass filter and then plot PSD using "pwelch" command. Problem is that I haven't used MATLAB before and have been struggling for past few days trying to get required results. I am attaching the images of the code,

Where Butterworth low pass filter is

and pwelch

But when I run the command the command I get two graphs only which don't provide enough information.

Kindly help me out in this.