The different processes involved in Chhath Puja are briefly summarized below.
The first day of the festival is meant for taking bath and eating food.
Observing fast for a whole day till the evening puja is involved in the second day of the festival.. The devotee (Vratti) does not consume food or water until the evening worship of Chhathi Maiya. Rasiao, made with puris or chapattis, is offered as Prasad to the Chhathi Maiya during evening worship and the same Prasad is used to break the day long fast of the Vratti.
Third day is for the preparation of Puja Samagri, Prasad and offerings that is required for Evening Arghya to Sun God.
The final process on the fourth day is to offer Morning offering or Bihaniya Arghya to Sun God. This day the rising sun is worshiped and the devotees break their 36-hour long fast. Then the Prasad is distributed among family and friends.