1213 Holy Baptism is the basis of the whole Christian life, the gateway to life in the Spirit (vitae spiritualis ianua),⁴ and the door which gives access to the other sacraments. Through Baptism we are freed from sin and reborn as sons of God; we become members of Christ, are incorporated into the Church and made sharers in her mission: "Baptism is the sacrament of regeneration through water in the word."

WHAT IS THIS SACRAMENT CALLED?
1214 This sacrament is called Baptism, after the central rite by which it is carried out: to baptize (Greek baptizein) means to "plunge" or "immerse"; the "plunge" into the water symbolizes the catechumen's burial into Christ's death, from which he rises up by resurrection with him, as "a new creature."
1215 This sacrament is also called "the washing of regeneration and renewal by the Holy Spirit," for it signifies and actually brings about the birth of water and the Spirit without which no one "can enter the kingdom of God."
1216 "This bath is called enlightenment, because those who receive this [catechetical] instruction are enlightened in their understanding . . . ." Having received in Baptism the Word, "the true light that enlightens every man," the person baptized has been "enlightened," he becomes a "son of light," indeed, he becomes "light" himself:
Baptism is God's most beautiful and magnificent gift. . . .We call it gift, grace, anointing, enlightenment, garment of immortality, bath of rebirth, seal, and most precious gift. It is called gift because it is conferred on those who bring nothing of their own; grace since it is given even to the guilty; Baptism because sin is buried in the water; anointing for it is priestly and royal as are those who are anointed; enlightenment because it radiates light; clothing since it veils our shame; bath because it washes; and seal as it is our guard and the sign of God's Lordship.

 WHO CAN RECEIVE BAPTISM?

1246 "Every person not yet baptized and only such a person is able to be baptized."

The Baptism of adults
1247 Since the beginning of the Church, adult Baptism is the common practice where the proclamation of the Gospel is still new. The catechumenate (preparation for Baptism) therefore occupies an important place. This initiation into Christian faith and life should dispose the catechumen to receive the gift of God in Baptism, Confirmation, and the Eucharist. 
1248 The catechumenate, or formation of catechumens, aims at bringing their conversion and faith to maturity, in response to the divine initiative and in union with an ecclesial community. The catechumenate is to be "a formation in the whole Christian life . . . during which the disciples will be joined to Christ their teacher. The catechumens should be properly initiated into the mystery of salvation and the practice of the evangelical virtues, and they should be introduced into the life of faith, liturgy, and charity of the People of God by successive sacred rites.
1249 Catechumens "are already joined to the Church, they are already of the household of Christ, and are quite frequently already living a life of faith, hope, and charity."⁴⁸ "With love and solicitude mother Church already embraces them as her own."

The Baptism of infants
1250 Born with a fallen human nature and tainted by original sin, children also have need of the new birth in Baptism to be freed from the power of darkness and brought into the realm of the freedom of the children of God, to which all men are called. The sheer gratuitousness of the grace of salvation is particularly manifest in infant Baptism. The Church and the parents would deny a child the priceless grace of becoming a child of God were they not to confer Baptism shortly after birth.
1251 Christian parents will recognize that this practice also accords with their role as nurturers of the life that God has entrusted to them.⁵²
1252 The practice of infant Baptism is an immemorial tradition of the Church. There is explicit testimony to this practice from the second century on, and it is quite possible that, from the beginning of the apostolic preaching, when whole "households" received baptism, infants may also have been baptized.

Catholic Catechism of the Catholic Church (CCCC)

"El santo Bautismo es fundamento de toda vida cristiana, el pórtico de la vida en el espíritu y la puerta que da acceso a los otros sacramentos. Por el Bautismo somos liberados del pecado y regenerados como hijos de Dios, llegamos a ser miembros de Cristo y somos incorporados a la Iglesia y hechos partícipes de su misión: 'El bautismo es el sacramento del nuevo nacimiento por el agua y la palabra.'"  - Catecismo de la Iglesia Católica #1213