The Sacrament of Confirmation confers special graces of the Holy Spirit upon the person being confirmed, just as such graces were granted to the Apostles on Pentecost. Like Baptism, therefore, it can only be performed once, and Confirmation increases and deepens all of the graces granted at Baptism.
The Catechism of the Catholic Church lists five effects of Confirmation:
The Sacrament of Confirmation requires extensive preparation.