Dear Daniel:
The anxiety is a result of certain connections or pathways in your brain, connections between neurons that get activated by this or that thought or perception. Once activated those pathways generate the anxiety. To physically disengage those pathways, you focus on your breath, air going in, air going out, and as your brain wonders (anxiety pathway re-activated) you go back to your breath. That way you give your anxiety provoking pathway a break and a chance to get your awareness away from it, to dis-identify with it and start a new pathway after the disengagement, a new focus. And you do it again and again.
Other than the breath you can focus on a sound, a sight, a smell, a touch… anything to take your attention away from the anxiety producing pathway, that is you disengage from it by engaging in a sound-related pathway (music, for example) or a touch related pathway (how this or that feels in my hand) etc.
anita