Speak unto the children of Israel: When a man or woman shall commit any sin that men commit, to commit a trespass against the L-RD, and that soul be guilty; then shall they confess their sin which they have done.”
– Numbers 5:6-7a, JPS 1917 Tanach
According to Rambam (Maimonides), this verse is the basis of vidui (confession), within the context of teshuvah (repentance). “And shall make reparation in full” (Numbers 5:7, JPS). This latter part of the pasuk (verse) denotes reparations made to others, if the aveirah (transgression) is against another person. It is interesting to note that the Hebrew word for reparation is from the same shoresh (root), shuv (to return) as teshuvah (repentance). Essentially, repentance is a return to H’Shem (the L-RD). “Let us return unto the L-RD” (Hosea 5:15b, JPS 1917 Tanach).
Such confession is a mandatory commandment. How is the verbal confession made? The sinner says thus: “I beseech Thee, O Great Name! I have sinned; I have been obstinate; I have committed profanity against Thee, particularly in doing thus and such. Now, behold! I have repented and am ashamed of my actions; forever will I not relapse into this thing again.” This is the elementary form of confession; but whosoever elaborates in confessing and extends this subject is, indeed, praise-worthy.
– Maimonides, Laws of Repentance; sefaria.org