The Move tool is used to move layers or selections. Moving layers is a simple procedure. Simply click with Button1 and drag the layer you wish to move. If you can see a layer underneath the active one, be sure to select the correct layer when moving. The pointer will by default indicate what will be moved.
The move tool can also be used to "nudge" the current layer in one pixel increments. To do so, select the layer that will be "nudged", focus the image window, and use the arrow keys. Ensure that Numlock is not turned on.
Default Keyboard Shortcut: M
The key combination: Shift-Button1 will move the currently selected layer regardless of which layer is visible.
The key combination: Alt-Button1 will move any available selection.