Press the Print Screen button. Open paint. Go to edit and select paste. Then save. That is the easiest way to create a screenshot. However, there are apps out here in the net that takes screenshots. Google for them.
It would help if you elaborated more on your question...
if you mean how can you make your dektop look like one in a screenshot, then you will have to find out which skins the author used in the screenshot and download them one by one and applying them.