From the 2002 General Introduction to the Roman Missal (GIRM) which can be accessed from
romanrite.com/girm.html :
*“The Act of Penitence *
51. Then the priest invites those present to take part in the Act of Penitence, which, after a brief pause for silence, the entire community carries out through a formula of general confession. The rite concludes with the priest’s absolution, which, however, lacks the efficacy of the Sacrament of Penance. On Sundays, especially in the Season of Easter, in place of the customary Act of Penitence, from time to time the blessing and sprinkling of water to recall Baptism may take place.
The Kyrie Eleison
52. After the Act of Penitence, the Kyrie is always begun, unless it has already been included as part of the Act of Penitence. Since it is a chant by which the faithful acclaim the Lord and implore his mercy, it is ordinarily done by all, that is, by the people and with the choir or cantor having a part in it. As a rule, each acclamation is sung or said twice, though it may be repeated several times, by reason of the character of the various languages, as well as of the artistry of the music or of other circumstances. When the Kyrie is sung as a part of the Act of Penitence, a trope may precede each acclamation.”