Move tool is actually understandable. There is no need to for further discussion. Move tool is use to move an element or a selection.
I use move tool after marquee. As I open an image, I will do selection of some of its parts with the help of the marquee tool. If you have read my last post, you will understand why.
According to Wikipedia, The marquee tool can make selections that are single row, single column, rectangular and elliptical. Once an area of an image is highlighted, the move tool can be used to manually relocate the selected piece to anywhere on the canvas.
Furthermore, move tool is not only use to move an image inside your canvas, but you can also move it from one canvas to another.