The acolyte is instituted for service at the altar and to assist the Priest and Deacon. It is his place principally to prepare the altar and the sacred vessels and, if necessary, to distribute the Eucharist to the faithful as an extraordinary minister.
In the ministry of the altar, the acolyte has his own proper functions (cf. nos. 187-193), which he must carry out in person.
The Functions of the Acolyte
187. The functions that the acolyte may carry out are of various kinds and several may occur at the same moment. Hence, it is desirable that these duties be suitably distributed among several acolytes. If, in fact, only one acolyte is present, he should perform the more important duties while the rest are to be distributed among several ministers.
The Introductory Rites
188. In the procession to the altar, the acolyte may carry the cross, walking between two ministers with lighted candles. Upon reaching the altar, however, the acolyte places the cross upright near the altar so that it may serve as the altar cross; otherwise, he puts it away in a dignified place. Then he takes his place in the sanctuary.
189. Through the entire celebration, it is for the acolyte to approach the Priest or the Deacon, whenever necessary, in order to present the book to them and to assist them in any other way required. Thus it is appropriate that, in so far as possible, the acolyte should occupy a place from which he can easily carry out his ministry either at the chair or at the altar.
The Liturgy of the Eucharist
190. In the absence of a Deacon, after the Universal Prayer and while the Priest remains at the chair, the acolyte places the corporal, the purificator, the chalice, the pall, and the Missal on the altar. Then, if necessary, the acolyte assists the Priest in receiving the gifts of the people and, if appropriate, brings the bread and wine to the altar and hands them to the Priest. If incense is being used, the acolyte presents the thurible to the Priest and assists him while he incenses the offerings, the cross, and the altar. Then the acolyte incenses the Priest and the people.
191. A duly instituted acolyte, as an extraordinary minister, may, if necessary, assist the Priest in distributing Communion to the people. If Communion is given under both kinds, in the absence of a Deacon, the acolyte administers the chalice to the communicants or holds the chalice if Communion is given by intinction.
192. Likewise, after the distribution of Communion is complete, a duly instituted acolyte helps the Priest or Deacon to purify and arrange the sacred vessels. In the absence of a Deacon, a duly instituted acolyte carries the sacred vessels to the credence table and there purifies them, wipes them, and arranges them as usual.
193. After the celebration of Mass, the acolyte and other ministers return together with the Deacon and the Priest in procession to the sacristy, in the same manner and in the same order in which they entered.
instructions are taken from USCCB/GIRM