The Move Tool moves/duplicates a selected image area or layer.
In the Toolbox, select the Move Tool
To move a layer* while no image area is selected, hold down the left mouse button,
drag and drop it (release the button).
To move a layer while some image
area is selected*, put the Move Tool outside the selection, then drag and drop.
To move a selected area put the Move Tool inside the selection, then drag and drop.
While the Move Tool is active, you can precisely move the selected
area or layer (if none is selected) using the keyboard cursor keys.
To constrain movement (to move an object strictly
horizontally or vertically) hold down [Shift]
key while moving.
To duplicate a layer drag it
with the Move Tool holding down [Alt] key.
To duplicate a selected area click
on it with the Move Tool and drag it holding down [Alt] key.
After you've moved / duplicated
the selection, the Move Tool moves / duplicates the selected area (not the entire layer),
no matter where the cursor is (movie).
Right-click click with the Move Tool on the image; there appears a list of all layers that are
not empty in this spot. Click on a layer name to select it.
Tip. Just in case you didn't know, the Move tool is also available in Photoshop Elements that is way cheaper version. And if you believe, Photoshop Elements lacks some other important feature, be sure to visit this page.