When you make a selection, you can move it around the screen in a couple of ways. First, you can put your mouse pointer inside the selection and drag it around your image canvas. The selection will retain its shape and size as it is moved, and it will relocate where ever you drop it (release the mouse button).

 

You can also move a selection with the arrow keys. Each time you press in arrow key, the selection will move a minute distance in the direction of the given arrow (up, down, left, or right). If you hold down an arrow key the selection will continuously move slowly in the given direction until you release the key. This can be a good way to fine tune the position of a selection.

 

 

If you want to move the selected part of an image, make a selection and then click the move tool. You can now drag the selected part of the image all around your image canvas with your mouse. You can even drag the selected part of the image to different image that you have open at the same time as shown in the graphic below.

 

 

Notice that when the selection is dragged to another image, it is added to that image as an additional layer (Layer 1 in this case).

 

Once again, to move the selection itself (the dashed border), just choose a marquee tool, click inside the selection, and drag it with your mouse. To move the part of the image that the selection contains, use the move tool.

 

Note: you can also drag just the selection (dashed border) to another image with your mouse if two images are open in Photoshop at the same time.