Some have the custom of performing the rite of kapparot [symbolic atonement] on the day preceding Yom Kippur; if it is not possible to do so then, the rite may be performed earlier.
The rite consists of taking a chicken in one's hand and reciting a prayer. A man takes a rooster; a woman takes a hen; a pregnant woman takes two fowls - a hen and a rooster. Optimally, the fowl should be white to symbolize purification from sin, as the verse (Isaiah 1:8) states: And if your sins be like scarlet, they shall become as white as snow. One should not, however, make an excessive effort to find a white fowl.
If a rooster or a hen is unavailable, one may substitute other fowl or animals; even a fish may be used for the rite. However, one should not use doves, since doves were brought as sacrificial offerings in the Temple, and this may give rise to the mistaken impression that the kapparot are a form of sacrifice.
The fowl [or other animal] used for kapparot is taken in the right hand and the appropriate text from the prayer book is recited. The bird is then passed over one's head three times and the appropriate text is recited.
The word kapparot [like kippur] means "atonement," and is used to refer to the chickens themselves, but one should not think that kapparot themselves serve as a source of atonement. Rather, they serve as a means to bring a person to the awareness that he might very well be deserving of death because of his sins and he will thereby be motivated to repent and ask G-d for mercy.
The fowl is then slaughtered in accordance with halachic procedure.
It is customary to redeem the kapparot for money, which is then given to the poor; some give the fowls themselves to the poor. Others perform the entire rite only with money, reciting the prescribed verses and giving the money to charity.