This is a combat stance, and is activated at the start of a Sequence, just after initiative is rolled. You can enter a stance as an action during a Sequence, but you can only do so when your shot is coming up. Stances stay in effect for one Sequence. Several stances can be combined. You can enter a stance in response to someone else's stance, so it may take a few moments for everyone to decide upon stances. You should describe how you dramatically shift into your stance, especially if you combine several stances.