A Sacrament is an outward sign instituted by Jesus Christ to give Grace.  The Sacraments have power to give Grace from the merits of Jesus Christ. 
Jesus gave outward signs to His Sacraments that both the Sacrament, and the Graces which it confers, may be easily recognized.  The outward sign of the Sacrament of Baptism is the pouring of the water and the speaking of the words at the same time: I baptize thee, etc.
The Grace which is conferred by the Sacrament of Baptism is the cleansing and sanctifying of the
soul.
Sanctifying Grace is the principal Grace conferred by the Sacraments. 
Some of the Sacraments give this Grace to the soul, and others increase it. 
Besides Sanctifying Grace, each Sacrament confers a special Grace called Sacramental Grace. 
The Sacramental Grace of the Sacrament of Penance, for example, is strength to avoid sin in the future.
Jesus instituted seven Sacraments: Baptism, Confirmation, Holy Eucharist, Penance, Extreme Unction, Holy Orders, and Matrimony.
 

Baptism and Penance are called THE SACRAMENTS OF THE DEAD:
       Because they take away original and mortal sin, which are the death of the soul
       Because they give Sanctifying Grace, which is its life.
Baptism, Confirmation, and Holy Orders can only be received once since they imprint an indelible mark on the soul. 
The power of the Sacraments does not depend upon the worthiness of those who administer them, but upon the merits of Jesus.  To obtain the Graces of the Sacraments, we must receive them worthily.

The Sacrament of Baptism cleanses the soul from Original Sin, makes us Christians, children of God, and heirs of Heaven.  “For as many of you as have been baptized in Christ, have put on Christ.” (Gal. 3:27).

The Sacrament of Baptism not only cleanses the soul from Original Sin, but also from all sins committed before Baptism. 
It also takes away the temporal and eternal punishments due to sin.  “Do penance, and be baptized every one of you in the name of Jesus Christ, for the remission of your sins.” (Acts 2:38).

Baptism is most necessary for salvation:
       Because  without it we cannot enter Heaven; and
       Because before it, no other Sacrament can be validly received.
“Amen, amen I say to thee, unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God.” (John 3:5).

Jesus instituted the Sacrament of Baptism when He declared to His Apostles: “Going therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.” (Matt. 28:19).
 
 

In case of necessity, ordinary natural water may be used, and anyone who has the use of reason may and should baptize.  Baptism can be received only once, because it imprints an indelible mark on the soul.