1) One breaths in a slow and relaxed manner, perhaps usually some other breathing exercise which is compatible, 2) awareness is paid to the breath; if thoughts arise they are gently set aside, 3) one counts up to five and then satrts at one again. If one has lost track, one simply starts at one again.
Rationale: The idea is to 'just breathe'. This tends to quiet and deepen and slow the breathing, and brings awareness of tension and holding. Counting is often prescribed for this purpose. Counting only to five and then returning to one provides an attentional reset soon enough to help busy Western minds from drifting.