What should be prepared for the procession? (GIRM 119) When the Entrance takes place with a procession, the following are also to be prepared: a Book of the Gospels; on Sundays and festive days, a thurible and incense boat, if incense is being used; the cross to be carried in procession; and candlesticks with lighted candles.

What is the order of the procession? (GIRM 120) When the people are gathered, the Priest and ministers, wearing the sacred vestments, go in procession to the altar in this order:

a) the thurifer carrying a smoking thurible, if incense is being used;
b) ministers who carry lighted candles, and between them an acolyte or other minister with the cross;
c) the acolytes and the other ministers;
d) a reader, who may carry a Book of the Gospels (though not a Lectionary), slightly elevated;
e) the Priest who is to celebrate the Mass.

If incense is being used, before the procession begins, the Priest puts some into the thurible and blesses it with the Sign of the Cross without saying anything.

What should be going on during the procession? (GIRM 121)
During the procession to the altar, the Entrance Chant takes place (cf. nos. 47-48). (GIRM 47) When the people are gathered, and as the Priest enters with the Deacon and ministers, the Entrance Chant begins. Its purpose is to open the celebration, foster the unity of those who have been gathered, introduce their thoughts to the mystery of the liturgical time or festivity, and accompany the procession of the Priest and ministers.

What is an Entrance Chant? (GIRM 48) This chant is sung alternately by the choir and the people or similarly by a cantor and the people, or entirely by the people, or by the choir alone. In the Dioceses of the United States of America there are four options for the Entrance Chant: (1) the antiphon from the Missal or the antiphon with its Psalm from the Graduale Romanum as set to music there or in another setting; (2) the antiphon and Psalm of the Graduale Simplex for the liturgical time; (3) a chant from another collection of Psalms and antiphons, approved by the Conference of Bishops or the Diocesan Bishop, including Psalms arranged in responsorial or metrical forms; (4) another liturgical chant that is suited to the sacred action, the day, or the time of year, similarly approved by the Conference of Bishops or the Diocesan Bishop.

What if the entrance antiphon is not sung? If there is no singing at the Entrance, the antiphon given in the Missal is recited either by the faithful, or by some of them, or by a reader; otherwise, it is recited by the Priest himself, who may even adapt it as an introductory explanation (cf. no. 31).

What is the importance of the incense, lighted candles, the cross, Book of the Gospel? Why are they chosen for the procession?

When does the procession or entrance end?  (GIRM 123)
The Priest goes up to the altar and venerates it with a kiss. Then, if appropriate, he incenses the cross and the altar, walking around the latter. Once all this has been done, the Priest goes to the chair. When the Entrance Chant is concluded, with everybody standing, the Priest and faithful sign themselves with the Sign of the Cross. The Priest says: In the name of the Father, and of the Son, and of the Holy Spirit. The people reply, Amen.

Why does the priest venerate the altar with a kiss?

After the Sign of the Cross what happens? (GIRM 124 & 50)
Then, facing the people and extending his hands, the Priest greets the people, using one of the formulas indicated. The Priest himself or some other minister may also very briefly introduce the faithful to the Mass of the day. [50] When the Entrance Chant is concluded, the Priest stands at the chair and, together with the whole gathering, signs himself with the Sign of the Cross. Then by means of the Greeting he signifies the presence of the Lord to the assembled community. By this greeting and the people’s response, the mystery of the Church gathered together is made manifest. After the greeting of the people, the Priest, or the Deacon, or a lay minister may very briefly introduce the faithful to the Mass of the day.

Why should the introduction, if done, be very brief?

What are the Kyrie eleison and the Gloria in excelsis? How should they be prayed? (GIRM 52 & 53) After the Penitential Act, the Kyrie, eleison (Lord, have mercy), is always begun, unless it hasalready been part of the Penitential Act. Since it is a chant by which the faithful acclaim the Lord and implore his mercy, it is usually executed by everyone, that is to say, with the people and the choir or cantor taking part in it. Each acclamation is usually pronounced twice, though it is not to be excluded that it 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 Penitential Act, a “trope” precedes each acclamation.

The Gloria in excelsis (Glory to God in the highest) is a most ancient and venerable hymn by which the Church, gathered in the Holy Spirit, glorifies and entreats God the Father and the Lamb. The text of this hymn may not be replaced by any other. It is intoned by the Priest or, if appropriate, by a cantor or by the choir; but it is sung either by everyone together, or by the people alternately with the choir, or by the choir alone. If not sung, it is to be recited either by everybody together or by two choirs responding one to the other. It is sung or said on Sundays outside Advent and Lent, and also on Solemnities and Feasts, and at particular celebrations of a more solemn character.

Why don’t we sing or say the Gloria during Advent and Lent?

What is the Collect and why is it important? (GIRM 127)
The Priest then calls upon the people to pray, saying, with hands joined, Let us pray. All pray silently with the Priest for a brief time. Then the Priest, with hands extended, says the Collect, at the end of which the people acclaim, Amen.