Over the years various versions of Kol Nidre have been adopted in various places. Indeed, the version found in most siddurim actually contain parts of each version. This stems from a machlokes (halachic dispute) over whether Kol Nidre is to annul vows from the past year (Babylonian traditional) or to declare annulled all vows of the coming year (European tradition, tosofot).
The two forms of confession, Al cheit and Ashamnu, alphabetically list all types of sins. The Al cheit, prayer lists many sins or categories of sins that are commonly committed. Sins are expressed in the plural not only to save individuals from embarrassment but so that the congregation as a whole might attain true atonement. One cannot confess only for oneself, rather one has to beg forgiveness for all Jews who sin. As the Rav Issac Luria, 16th Century Kabbalist, wrote that confession is written in the plural, "We have sinned because all Israel is considered like one body and every person is a limb of that body. So we confess to all the sins of all the parts of our body.
If you read the Al cheit carefully, you will see that the list of sins is not a list of the Mitzvot. Rather, it is a list of categories of sins that are the most common. Many relate to our misuse of speech and having the wrong type of thoughts or attitude. Some have to do with more concrete mitzvot like shabbat or Kashrut. All relate to us in way or another. Of course, one should not feel limited to confess only the list of sins printed in the siddur, one should mention viduy any specific sins which he or she may have committed. It is customary to gently beat ones chest during the viduy, as if to say that your heart may have led you astray in the past but hopefully, this will not happen in the future.
On Yom Kippur, yet a fifth service (the only day of the year with 5) is added. The extra service unique to Yom Kippur is called Neilah.
Neilah is said after Mincha as the sun is going down and literally means closing (or locking) and refers to either the closing of the gates of the Holy Temple at the end of the day or it refers to the closing of the gates of prayer as Yom Kippur is ending .
The Neilah service contains stirring pleas that our prayers be accepted by G-d before Yom Kippur ends. The heavenly judgment inscribed on Rosh Hashanah is now sealed during Neilah. The chazan chants the service in a special melody designed to stir the emotions and bring the congregation to greater devotion.
There are a number of customs that have become well accepted in connection with Neilah. Usually the Rabbi or Rosh Yeshiva (head of Jewish studies school) or the Village Elder will speak before the Neilah service to inspire the congregants to pray more fervently. In many congregations he will himself lead the service instead of the cantor - again - expressing the hightened sence of urgency.
The Aron HaKodesh (Holy Ark that contains
the congregation's Torah scrolls) is kept open for the entire service. Those able to stand
up for the entire time, do so.
Following Neilah, the shofar is sounded with one great and mighty long blast and the services conclude with the exclamations of Shema Yisrael - Hear Oh Israel and Next Year In Jerusalem - LeShana Haba BiYerushalayim...
The High Priest's Temple Service