No one's giving me info on this, either, so this is all speculation..
-There's a quest you do to get the ability from Taz-Hiz (PoR version, not LDoN).
-All classes get either a spell or aura.. some get both. Rangers, as an exception with a badly bugged trap, get a Chromatic (-30) check root spell instead of either.
-You activite them, like an activated AA ability. This sets them in a position.
-Once a MOB (not sure if the MOB has to have you on its agro list, be KOS, or just any.. or however this works) sets over it, the trap expends itself as an (AoE?) spell with whatever effect it should.
-You may have only one trap up at a time.
-There are two ranks of the trap, depending on which task you did to get it. A level 55 and a level 70 version.
-Traps likely cost stanima to place, as a one-time stanima fee.