the way a Stance is used is:
1) Play the Stance from your hand
2) Apply its damage, take wounds, at that moment.
3) Leave it in Play forever without the need of an upkeep cost(do not remove it in Cleanup, if no triggering occured)
4) You are obliged to Trigger it when the Trigger effect happens
5) Send it to discards after Triggering
Thanks in advance!
This is accurate.
The single additional piece worth mentioning is that if you play another Stance you discard the Stance you already have in play without dealing with its Trigger effect.