Open the main picture that you want to form part of the composite image. In this case we have selected the owl, with a feathering value of 0.2 pixels to give a very hard edge. 
Once you are happy with your selection go to the Edit Menu and click on Copy. This temporarily places the area that you have selected onto the Photoshop "Clipboard" and allows you to paste it into another picture. 
Minimise this image incase you need to make changes to your selection
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