Placing
With the wand
/nxh wand <hologram> gives you a wand. Right-click a block: that block becomes the hologram's top-left corner, facing the way the block face does, so it works on walls, floors and ceilings. Sneak and right-click to undo your last placement.
In front of you
/nxh place <hologram> puts one right in front of you, facing you.
Moving and removing
/nxh removelists the holograms nearest you, each with a [Remove] button./nxh remove <hologram>removes one; press Tab to pick it, nearest first./nxh teleport <hologram>takes you to the front of one. Placed more than once? Tab after the name lists where, nearest first./nxh movehere <hologram>moves one in front of you./nxh moveto <hologram> <x> <y> <z>moves its centre to a spot.~means where you stand.
The same hologram can be placed as many times as you like. Editing it in the editor changes every copy.