Shulchan Aruch Chapter 607:
The arrangement of וידוי (the confession prayer) in מנחה (Mincha) on Erev Yom Kippur
Note: The REMA is in brackets 
1. It is necessary to say the confession (וידוי) in Mincha before the dividing meal (סעודה המפסקת). [The individual should say it after he completed his prayer (the 18 blessings) and the Chazzan should say it on Yom Kippur within the prayer.]
2. It is not necessary to detail the sin. But if you want to detail the sin, you may do so. If one is confessing quietly, it is proper to detail the sin. [But if you are praying loudly, or when the Chazzan is going over the prayer, the sin should not be elucidated. That which we say “on the sin....” (אל חטא) outlined one after the other is not considered detailing (the sin) even though everyone says the same thing; it is nothing more than the customary arrangement (נוסח) of the prayer.]
3. It is necessary to confess standing. Even when already confessed and are hearing it from the Chazzan, you must stand [and we repeat the confession with the Chazzan. The main part of the confession is “but we have sinned”.]
4. Sins that you already confessed on the past Yom Kippur and you did not do them since, nevertheless, you are able to confess them again.
5. In the afternoon prayer (מנחה) on Erev Yom Kippur, we do not finish with another confession (וידוי) [and the Chazzan does not repeat the confession in Mincha, but prays 18 (blessings) like usual. And we don’t say “our father, our king” (אבינו מלכינו) and of course, תחנון].
6. The entire congregation is struck with the “forty lashes” (מלקות ארבעים) after Mincha since it will cause a man’s heart to repent from his sins. [The custom is for the receiver to say confessions when he is being struck and for the smiter to say ...והוא רחום יכפר עון three times since it contains thirty nine words just like the thirty nine lashes. The custom is to give the lashes with a leather strap any (small) amount since it only serves as a rememberance for the real lashes. You should take a strap made from a calf since it says “ידע שׁור קונהו” and the receiver should not stand or sit but his face should be bent over facing north and his back is facing south. Yom Kippur only forgives the transgressions that one sincerly attoned for. But if one prayed on Yom Kippur but thought in his heart “what good is this?”, Yom Kippur does not attone for him.]
Translated by Jay Dinovitser
 The afternoon prayer, מנחה
 M.B: But on Erev Yom Kippur, at Mincha (the evening prayer), the Chazzan does not say it when he repeats the prayer as explained later on in paragraph 5.
 Kittzur S.A: This is praiseworthy as stated in Psalms 51:5 “and my sin is always in front of me”.
 M.B: Although it is called “forty lashes”, only 39 are given by tradition.
 This is translated according to the Mishna Brura. Also, it does not need to be a fist breath wide.
 Lit. “on it”