1. The Order of Vidui (Confessing) at Minchah of Erev Yom Kippur, 6 Seifim: One must say vidui at minchah prior to the final meal before the fast. RAMA: Someone by himself says it after he finishes his prayer (i.e. the amidah) and the chazan says it on Yom Kippur during his prayer (amidah)(Tur).
2. One need not specifically detail his sin. But if one wants to specify, he may decide to do so. Silent confession is appropriate for specifying the sin. RAMA: However, when he prays out loud, or for the chazan when he repeats the amidah, the sin is not specified. That which we say, the Al Chet prayer, does not specify the person's specific sin. Everyone says it equally according to the nusach of the prayer.[Note: meaning, since everyone recites this confessional uniformly, it is considered as part of the standard prayer service. It may therefore be recited aloud.]
3. One must confess while standing. Even when he hears it from the chazan and he already confessed, he must stand. RAMA: And he must go back and confess again with the chazan (Ra"n). The essence of the vidui is "but we have sinned". (Tur)
4. Regarding sins for which one confessed on the previous Yom Kippur and did not repeat, he may confess them again.
5. During mincha on Erev Yom Kippur, one does not complete the confession with a blessing. RAMA: and the chazan does not repeat the vidui at minchah; rather he says the shmoneh esrei like the other days of the year (Tur and Mordechai) and Avenu Malkeinu is not recited, and obviously Tachanun is not said.
6. All of the congregation receives 40 lashes after minchah, for from this one places on his heart to repent for his sins. RAMA: The custom is for the recipient of lashes to say confessions at the time he is lashed and the one who lashes says "and He who is merciful atones for sin", etc. three times, summing to 39 words corresponding to the 39 lashes. It is the custom to use a strap of any width, for these lashes are only remembrance of lashes. One takes a strap of calf's leather; [this] spurs one to repentance by [recalling] the verse, “[Even] an ox knows its master….” (Kol Bo). The one who is lashed neither stands nor sits but should crouch forward with his face to the north and his back to the south (Maharil). Yom Kippur atones only for those who repent and believe in the atonement it conveys. If a person holds it in disdain and thinks in his heart, “What will Yom Kippur do for [me]?” — Yom Kippur will not atone for him. (Rambam Perek 3 Hilchos Shegagos).