How do I select individual elements or layers?

In order to select individual elements or layers, you will need to use the Selection tool  to double-click on the image/element you want to select. Individual layers should then be selected (in a thin red line) and free to drag, stretch, or delete. 

So, for instance, if you were editing an image of a face, you would need to double-click your Selection tool in order to remove, drag, or alter the face, the eyes, the mouth, etc.