Shitala Satam is observed on Shravan Krishna Paksha Saptami in Gujarat and most of parts in India. This day is dedicated to Goddess Shitala Maa. It's observed by Married women for the welfare of family and specially for childrens to escape from small pox. Puja of Shitala mata is the main ritual performed on this and women do this puja after taking bath with cold water. Food is cooked on previous day and It's called as a "Randhan Chhat" and that cook is eaten on the Shitala Satam day.
You can Perform Puja of Shitala Maata with this Mantra:
शीतले हर में पापं, पुत्रा पुत्र सुखप्रदे |
धन धान्यप्रदे देवी, पूजांगृहान नमोस्तुते ||
You can distribute food to poor people on Shitala Satam.