From the Catechism:
II. THE LAY FAITHFUL
897 "The term 'laity' is here understood to mean all the faithful except those in Holy Orders and those who belong to a religious state approved by the Church. That is, the faithful, who by Baptism are incorporated into Christ and integrated into the People of God, are made sharers in their particular way in the priestly, prophetic, and kingly office of Christ, and have their own part to play in the mission of the whole Christian people in the Church and in the World."
The vocation of lay people
898 "By reason of their special vocation it belongs to the laity to seek the kingdom of God by engaging in temporal affairs and directing them according to God's will.... It pertains to them in a special way so to illuminate and order all temporal things with which they are closely associated that these may always be effected and grow according to Christ and maybe to the glory of the Creator and Redeemer."
899 The initiative of lay Christians is necessary especially when the matter involves discovering or inventing the means for permeating social, political, and economic realities with the demands of Christian doctrine and life. This initiative is a normal element of the life of the Church:
Lay believers are in the front line of Church life; for them the Church is the animating principle of human society. Therefore, they in particular ought to have an ever-clearer consciousness not only of belonging to the Church, but of being the Church, that is to say, the community of the faithful on earth under the leadership of the Pope, the common Head, and of the bishops in communion with him. They are the Church.
900 Since, like all the faithful, lay Christians are entrusted by God with the apostolate by virtue of their Baptism and Confirmation, they have the right and duty, individually or grouped in associations, to work so that the divine message of salvation may be known and accepted by all men throughout the earth. This duty is the more pressing when it is only through them that men can hear the Gospel and know Christ. Their activity in ecclesial communities is so necessary that, for the most part, the apostolate of the pastors cannot be fully effective without it.
The participation of lay people in Christ's priestly office
901 "Hence the laity, dedicated as they are to Christ and anointed by the Holy Spirit, are marvellously called and prepared so that even richer fruits of the Spirit maybe produced in them. For all their works, prayers, and apostolic undertakings, family and married life, daily work, relaxation of mind and body, if they are accomplished in the Spirit - indeed even the hardships of life if patiently born - all these become spiritual sacrifices acceptable to God through Jesus Christ. In the celebration of the Eucharist these may most fittingly be offered to the Father along with the body of the Lord. And so, worshipping everywhere by their holy actions, the laity consecrate the world itself to God, everywhere offering worship by the holiness of their lives."
902 In a very special way, parents share in the office of sanctifying "by leading a conjugal life in the Christian spirit and by seeing to the Christian education of their children."
903 Lay people who possess the required qualities can be admitted permanently to the ministries of lector and acolyte. When the necessity of the Church warrants it and when ministers are lacking, lay persons, even if they are not lectors or acolytes, can also supply for certain of their offices, namely, to exercise the ministry of the word, to preside over liturgical prayers, to confer Baptism, and to distribute Holy Communion in accord with the prescriptions of law."
Participation in Christ's prophetic office
904 "Christ . . . fulfills this prophetic office, not only by the hierarchy . . . but also by the laity. He accordingly both establishes them as witnesses and provides them with the sense of the faith [sensus fidei] and the grace of the word"
To teach in order to lead others to faith is the task of every preacher and of each believer.
905 Lay people also fulfill their prophetic mission by evangelization, "that is, the proclamation of Christ by word and the testimony of life." For lay people, "this evangelization . . . acquires a specific property and peculiar efficacy because it is accomplished in the ordinary circumstances of the world."
This witness of life, however, is not the sole element in the apostolate; the true apostle is on the lookout for occasions of announcing Christ by word, either to unbelievers . . . or to the faithful.
906 Lay people who are capable and trained may also collaborate in catechetical formation, in teaching the sacred sciences, and in use of the communications media.
907 "In accord with the knowledge, competence, and preeminence which they possess, [lay people] have the right and even at times a duty to manifest to the sacred pastors their opinion on matters which pertain to the good of the Church, and they have a right to make their opinion known to the other Christian faithful, with due regard to the integrity of faith and morals and reverence toward their pastors, and with consideration for the common good and the dignity of persons."
Participation in Christ's kingly office
908 By his obedience unto death, Christ communicated to his disciples the gift of royal freedom, so that they might "by the self-abnegation of a holy life, overcome the reign of sin in themselves":
That man is rightly called a king who makes his own body an obedient subject and, by governing himself with suitable rigor, refuses to let his passions breed rebellion in his soul, for he exercises a kind of royal power over himself. And because he knows how to rule his own person as king, so too does he sit as its judge. He will not let himself be imprisoned by sin, or thrown headlong into wickedness.
909 "Moreover, by uniting their forces let the laity so remedy the institutions and conditions of the world when the latter are an inducement to sin, that these may be conformed to the norms of justice, favoring rather than hindering the practice of virtue. By so doing they will impregnate culture and human works with a moral value."
910 "The laity can also feel called, or be in fact called, to cooperate with their pastors in the service of the ecclesial community, for the sake of its growth and life. This can be done through the exercise of different kinds of ministries according to the grace and charisms which the Lord has been pleased to bestow on them."
911 In the Church, "lay members of the Christian faithful can cooperate in the exercise of this power [of governance] in accord with the norm of law." And so the Church provides for their presence at particular councils, diocesan synods, pastoral councils; the exercise in solidum of the pastoral care of a parish, collaboration in finance committees, and participation in ecclesiastical tribunals, etc.
912 The faithful should "distinguish carefully between the rights and the duties which they have as belonging to the Church and those which fall to them as members of the human society. They will strive to unite the two harmoniously, remembering that in every temporal affair they are to be guided by a Christian conscience, since no human activity, even of the temporal order, can be withdrawn from God's dominion."
913 "Thus, every person, through these gifts given to him, is at once the witness and the living instrument of the mission of the Church itself 'according to the measure of Christ's bestowal."'