Confirmation is a Sacrament instituted by Jesus Christ as a complement to Baptism. As there is a sacrament of spiritual birth, so there is a sacrament of spiritual virility, conferring the grace required for growth in good will, fidelity, and Christian courage.
Not explicitly. But we know that the Apostles conferred the gift of the Holy Spirit by the laying on of hands in a sacramental rite distinct from Baptism. Acts VIII., 14-17. They would not have confirmed the faithful by this distinct right unless they had been commissioned to do so by Christ. Christian tradition and the authoritative teaching of the Catholic Church are absolute guarantees that Confirmation is a genuine Christian Sacrament.
No. But it would be wrong and sinful to neglect it through indifference. Christ certainly did not institute this Sacrament needlessly. It confers graces of the utmost use in the spiritual life, rendering us stronger in the struggle for virtue, and therefore rendering our salvation the more assured.