Select the Marquee tool. Using that click and drag a square or rectangle around the portion of picture you wish to duplicate. Once you have done that, hit Ctrl+C. Now from the top menu bar select layer, new layer. Once it is created switch to the new layer. Hit Ctrl+P. Now you should have a layer with only the section of photo you wanted to reproduce. You can now manipulate this section to your heart's content. Move it around, add filters, whatever tickles your pickle. I hope that helps.