If you practice noticing your breathing for a few minutes at a time you will also notice that you are particularly aware of the breath at a particular place in your body. Typical points of awareness are the tip of your nostrils, just inside your nostrils, in your chest, your diaphragm (between rib-cage and tummy) or your tummy.
When you find this place you can think of it as an anchor point that can "anchor" you to awareness for short periods of time. If your attention is a boat drifting on the water or tossed around by the waves, mindfulness can be the anchor that holds you in place. You can get straight into mindfulness by going to your anchor point.
In a busy office, a crowded street, a noisy kitchen - whatever the circumstances - bringing your awareness to your anchor point will give you a sense of presence of mind, a steadiness, in the swirl of events, emotions and thoughts.