Align
Ctrl+Shift+Alt+Arrows
Aligns all selected shapes on the active page with the superselected one (note: a superselected shape is the first shape selected in a group. Visio identifies it whith a ticker pink border in a selection).
Example - Align Top (see image):
Assuming the white square is the superselected one, doing a "align to top" with these shapes selected would result in the grey shapes being moved so that their tops are aligned with the top of the white square shape.
Juxtapose
Aligns all selected shapes on the active page with the edge of thesuperselected one.
Example - Juxtapose Right (see image):
Assuming the white square is the superselected shape, doing a "juxtapose right" with these shapes selected would result in the grey shapes being moved so that their leftmost edge are aligned with the white shape's rightmost edge.
Serial Juxtapose
Starting from the top, left, bottom or rightmost shape in a selection (depending on the command), aligns subsequent shapes with their nearest neighbor's edge (again, direction depends on the chosen command).
Example - Serial Juxtapose Right (see image):
Assuming the white square is the leftmost shape before triggering the "serial juxtapose right" command (the superselected shape does not matter), the grey rectangle is moved so that its left edge is aligned with the white shape's right edge and subsequently the grey circle is moved so that its left edge is aligned with the grey rectangle's right edge
Distribute
Repositions the selected shapes so that an equal amount of space (vertical or hirizontal) exists between them, regardless of their relative size.
Example - Distribute Horizontal (see image):
Assuming the grey rectangle was closer to the white circle than to the square before using the command, it has now been moved so that it is exactly equidistant between the other two selected shapes.
Order
Moves the selected shapes closer or farther away from the topmost layer of a page. This either partially or completely hides those shapes behing other shapes or reveals them.
Example - Bring Forward (see image):
Assuming the white square was behind both the rectangle and circle before using the command, selecting it and doing a "bring forward" moves it one step closer to the top layer of the document. Doing the command again would bring it in front of the circle as well.