What the vrata is
Satyanarayana Pooja is a vrata — a vow observed with a specific intent. It is most often performed as an act of gratitude: after a new job, a recovery, a marriage, a house purchase, or simply on a Purnima to keep the household settled.
When it is performed
Purnima is the classic day. Ekadashi, Sankranti and the day after a significant event are also common. It can be performed on any day when there is a reason for gratitude; there is no prohibition.
What happens
The pooja opens with Ganapati worship and the sankalpa in the family's gotra. The Satyanarayana Swamy is invoked in a kalasha or an image, and shodashopachara — sixteen forms of hospitality — are offered. The centre of the vrata is the katha, read in five chapters, each telling of someone who kept or broke the vow.
The prasadam is sapatha — wheat rava, sugar or jaggery, ghee and banana, in equal measure. It is offered and then shared; traditionally no one leaves without receiving it.
Fasting
The person performing the vrata fasts from morning until the pooja concludes. Fruit and milk are permitted. The fast is broken with the prasadam.
Family participation
The couple sits together for the sankalpa. Children and elders join for the katha and aarti. There is no restriction on who may attend.