From the documentation, pasted only parts referring to the discussed topic:
<map name>,<x>,<y>,<facing>%TAB%script%TAB%<NPC Name>%TAB%<sprite id>,<triggerX>,<triggerY>,{<code>}
A '-1' Sprite ID will make the NPC invisible (and unclickable).
TriggerX and triggerY, if given, will define an area, centered on NPC and
spanning triggerX cells in every direction across X and triggerY in every
direction across Y. Walking into that area will trigger the NPC. If no
'OnTouch:' special label is present in the NPC code, the execution will start
from the beginning of the script, otherwise, it will start from the 'OnTouch:'
label. Monsters can also trigger the NPC, though the label 'OnTouchNPC:' is
used in this case.
Thus, taking @Poring King's first example, you would declare the NPC like this I think
prontera,0,0,3 script TouchMe -1,11,11{