In and out through the nose, directing your breath right down into your tummy (expanding the belly).
Notice how you feel.
Alternate nose breathing - https://www.artofliving.org/au-en/yoga/breathing-techniques/alternate-nostril-breathing-nadi-shodhan
Diaphragmatic breathing - this may also be known as deep belly breathing, where the diaphragm contracts and the belly expands (Buddha belly). The breath is going all the way down to the tummy, a deep calming breath, as opposed to the short, shallow chest breathing. It is nice to place both hands on the tummy and feel the expansion on the inhalation and the contracting on the exhalation, as the navel comes back towards the spine.
(Image Source: Unknown)