The Gloria
53. The Gloria is a very ancient and venerable hymn in which the Church, gathered together 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 text. The Gloria 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 all together or by two parts of the congregation responding one to the other.
It is sung or said on Sundays outside the Seasons of Advent and Lent, on solemnities and feasts, and at special celebrations of a more solemn character.
The Collect
54. Next the priest invites the people to pray. All, together with the priest, observe a brief silence so that they may be conscious of the fact that they are in God's presence and may formulate their petitions mentally. Then the priest says the prayer which is customarily known as the collect and through which the character of the celebration is expressed. In accordance with the ancient tradition of the Church, the collect prayer is usually addressed to God the Father, through Christ, in the Holy Spirit, and is concluded with a trinitarian ending, that is to say the longer ending, in the following manner:If the prayer is directed to the Father: Per Dominum nostrum Iesum Christum Filium tuum, qui tecum vivit et regnat in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum (Through our Lord, Jesus Christ, your Son, who lives and reigns with you and the Holy Spirit, one God, forever and ever);
If it is directed to the Father, but the Son is mentioned at the end: Qui tecum vivit et regnat in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum (Who lives and reigns with you and the Holy spirit, one God, forever and ever);
If it is directed to the Son: Qui vivis et regnas cum Deo Patre in unitate Spiritus Sancti, Deus, per omnia saecula saeculorum (You live and reign with God the Father in the unity of the Holy Spirit, one God, forever and ever).
The people, uniting themselves to this entreaty, make the prayer their own with the acclamation, Amen.
There is always only one collect used in a Mass.
B. The Liturgy of the Word
55. The main part of the Liturgy of the Word is made up of the readings from Sacred Scripture together with the chants occurring between them. The homily, Profession of Faith, and Prayer of the Faithful, however, develop and conclude this part of the Mass. For in the readings, as explained by the homily, God speaks to his people, opening up to them the mystery of redemption and salvation, and offering them spiritual nourishment; and Christ himself is present in the midst of the faithful through his word. By their silence and singing the people make God's word their own, and they also affirm their adherence to it by means of the Profession of Faith. Finally, having been nourished by it, they pour out their petitions in the Prayer of the Faithful for the needs of the entire Church and for the salvation of the whole world.
Silence
56. The Liturgy of the Word is to be celebrated in such a way as to promote meditation, and so any sort of haste that hinders recollection must clearly be avoided. During the Liturgy of the Word, it is also appropriate to include brief periods of silence, accommodated to the gathered assembly, in which, at the prompting of the Holy Spirit, the word of God may be grasped by the heart and a response through prayer may be prepared. It may be appropriate to observe such periods of silence, for example, before the Liturgy of the Word itself begins, after the first and second reading, and lastly at the conclusion of the homily.
From: GENERAL INSTRUCTION OF THE ROMAN MISSAL