It is customary to conduct "Hatarat Nedarim" – the formal annulment of vows – before Rosh Hashanah and before Yom Kippur. This declaration is made in the presence of three people that serve as a Bet Din (Rabbinical court). It absolves a person from vows he made and from customs which he accepted upon himself. Preferably, a person should perform Hatarat Nedarim in the presence of ten men, as this kind of Bet Din has more authority than a three-member Bet Din.
As part of the Hatarat Nedarim declaration, a person says that although Halacha requires a person to specify the particular vows which he wishes to annul, he is unable to do so because they are too numerous. The work Derech Ha’haim cites from the Shiboleh Ha’leket (Rav Sidkiya Ben Abraham, Italy, 1230-1300) that this special provision applies only to vows of which a person is unaware. One can earn annulment for these vows by informing the Bet Din that he cannot recall his vows. If, however, a person is aware of a certain vow or custom from which he wishes to absolve himself, then he must specify it when he makes the Hatarat Nedarim declaration.
Both men and women are required to make Hatarat Nedarim. Customarily, however, a husband represents his wife when he stands before the Bet Din for Hatarat Nedarim. In fact, the text that we use explicitly mentions that one seeks absolution of his own vows as well as the vows of his wife. Furthermore, women customarily attend the Kol Nidreh service on Yom Kippur, which is also effective in annulling one’s vows.
Hatarat Nedarim does not annul one’s vows if he does not understand the text he recites. Unfortunately, many people recite the Hebrew text without understanding what they say, mistakenly thinking that this is some form of ritual that they must perform before the new year. A person who does not understand the Hebrew text must recite Hatarat Nedarim in a language he understands, for otherwise his declaration is meaningless.
The Hatarat Nedarim declaration also includes a clause voiding in advance all future vows. This provision affects only vows that one takes during the next year without remembering having made this stipulation. If a person takes a vow even though he was fully cognizant of the fact that he made this stipulation before Rosh Hashanah, then the vow is binding, and he must perform Hatarat Nedarim if he wishes to have it annulled. It should be noted that even if one uttered a vow without remembering the stipulation made on Ereb Rosh Hashanah, in which case the vow technically is not binding, it is nevertheless customary to treat the vow as binding, and conduct Hatarat Nedarim.
Summary: It is customary to conduct Hatarat Nedarim before Rosh Hashanah and Yom Kippur. This applies to both men and woman, but husbands generally represent their wives when making Hatarat Nedarim. One who knows of specific vows he made or customs he accepted for which he seeks annulment must specify them during Hatarat Nedarim. It should be read in a language in which one understands.