Do you mean,  you want to   get  objects  perfectly stacked  so  the top  of  one  just  touches the  bottom  of the next one?

 If  so,  you can  do this like this:

 -  Select  them  all
 -  In  the ` align`  window,  switch it  to `align  to  key  object`
 -  Make  sure the numbers box is set to 0
 -  Hit  the ` distribute  objects  vertically`  button in the bottom  left of  the panel

This  puts everything  in a stack based  on  the  stacking order ,  where  the distance  between  each object is the number in the box.  If  they're  in the  wrong order, re-`arrange`  which objects  are on top of each other.

This stacks any number of objects:

![enter image description here][1]

----

That said, if you're just making simple arrows, there's an easier way using the **arrowheads** options on the `Stroke` window. I think in versions earlier than CS6, arrowhead options were  buried in the `Effects` menu somewhere. If you can't see these options, hit "Show options" in the flyout menu at the top right of the box (Adobe love hiding useful tools without leaving any clue that they are there):

![enter image description here][2]


  [1]: https://i.sstatic.net/GwhOY.png
  [2]: https://i.sstatic.net/kPxe7.png