YOU WILL F
The Lector at Mass 
General Principles
Reading and Explaining the Word of God
When the Sacred Scriptures are read in the Church, God himself speaks to his people, and Christ, present in his word, proclaims the Gospel. Therefore, the readings from the Word of God are to be listened to reverently by everyone, for they are an element of the greatest importance in the Liturgy. Although in the readings from Sacred Scripture the Word of God is addressed to all people of whatever era and is understandable to them, a fuller understanding and a greater efficaciousness of the word is nevertheless fostered by a living commentary on the word, that is, by the Homily, as part of the liturgical action. (General Instruction of the Roman Missal [GIRM], no. 29)
Vocal Expression of the Different Texts
In texts that are to be pronounced in a loud and clear voice, whether by the Priest or the Deacon, or by a reader, or by everyone, the voice should correspond to the genre of the text itself, that is, depending upon whether it is a reading, a prayer, an explanatory comment, an acclamation, or a sung text; it should also be suited to the form of celebration and to the solemnity of the gathering. Consideration should also be given to the characteristics of different languages and of the culture of different peoples. (GIRM, no. 38)
Silence
The Liturgy of the Word is to be celebrated in such a way as to favour meditation, and so any kind of haste such as hinders recollection is clearly to be avoided. In the course of it, brief periods of silence are also appropriate, accommodated to the assembled congregation; by means of these, under the action 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. (GIRM, no. 56)
Scripture Readings
In the readings, the table of God’s Word is spread before the faithful, and the treasures of the Bible are opened to them. Hence, it is preferable that the arrangement of the biblical readings be maintained, for by them the unity of both Testaments and of salvation history is brought out. Nor is it lawful to replace the readings and Responsorial Psalm, which contain the Word of God, with other, non-biblical texts.
In the celebration of the Mass with the people, the readings are always read from the ambo.
The function of proclaiming the readings is by tradition not presidential but ministerial. Therefore, the readings are to be read by a reader, but the Gospel by the Deacon or, in his absence, by another Priest. If, however, a Deacon or another Priest is not present, the Priest Celebrant himself should read the Gospel, and moreover, if no other suitable reader is present, the Priest Celebrant should also proclaim the other readings as well.
After each reading, whoever reads it pronounces the acclamation, and by means of the reply the assembled people give honour to the Word of God that they have received in faith and with gratitude. (GIRM, nos. 57-59)
The lector is instituted to proclaim the readings from Sacred Scripture, with the exception of the Gospel. He may also announce the intentions for the Universal Prayer and, in the absence of a psalmist, recite the Psalm between the readings.
In the celebration of the Eucharist, the lector has his own proper function (cf. nos. 194-198), which he himself must carry out. (GIRM, no. 99)
In the absence of an instituted lector, other lay people may be deputed to proclaim the readings from Sacred Scripture, people who are truly suited to carrying out this function and carefully prepared, so that by their hearing the readings from the sacred texts the faithful may conceive in their hearts a sweet and living affection for Sacred Scripture. (GIRM, no. 101)
The Liturgy of the Word
After the Collect, all sit. The Priest may, very briefly, introduce the faithful to the Liturgy of the Word. Then the reader goes to the ambo and, from the Lectionary already placed there before Mass, proclaims the First Reading, to which all listen. At the end, the reader pronounces the acclamation “The word of the Lord”, and all reply, “Thanks be to God”.
Then a few moments of silence may be observed, if appropriate, so that all may meditate on what they have heard.
Then the psalmist or the reader proclaims the verses of the Psalm and the people make the response as usual.
If there is to be a Second Reading before the Gospel, the reader proclaims it from the ambo. All listen and at the end reply to the acclamation, as noted above (no. 128). Then, if appropriate, a few moments of silence may be observed. (GIRM, nos. 128-130)
Functions of the Lector
The Introductory Rites
In the procession to the altar, in the absence of a Deacon, the reader, wearing approved attire [see GIRM, no. 339], may carry the Book of the Gospels, slightly elevated. In that case, the reader walks in front of the Priest but otherwise walks along with the other ministers.
Upon reaching the altar, the reader makes a profound bow with the others [see also GIRM, no. 274]. If he is carrying the Book of the Gospels, he approaches the altar and places the Book of the Gospels upon it. Then the reader takes his own place in the sanctuary with the other ministers. (GIRM, nos. 194-195)
The Liturgy of the Word
The reader reads from the ambo the readings that precede the Gospel. In the absence of a psalmist, the reader may also proclaim the Responsorial Psalm after the First Reading.
In the absence of a Deacon, the reader, after the introduction by the Priest, may announce the intentions of the Universal Prayer from the ambo.
If there is no singing at the Entrance or at Communion and the antiphons given in the Missal are not recited by the faithful, the reader may read them at an appropriate time (cf. nos. 48, 87). (GIRM, nos. 196-198)
The Concluding Rites
At the conclusion of the Mass, the lector does not process with the Book of the Gospels. The Lectionary is never carried in procession. The lector may join in the procession at the end of Mass in the same order as in the procession to the altar.
(Source: USCCB)