By the consecration the transubstantiation of the bread and wine into the Body and Blood of Christ is brought about. Under the consecrated species of bread and wine, Christ himself, living and glorious, is present in a true, real, and substantial manner: his Body and his Blood, with his soul and his divinity.
[1413, Catechism of the Catholic Church]
Adults prepare for the Sacrament of Reconciliation (Penance) and the Sacrament of the Eucharist as part of the Rite of Christian Initiation of Adults (RCIA).
When receiving Holy Communion in the hand, the priest elevates the Sacred Host and says "The Body of Christ." The person receiving Holy Communion responds "Amen" and steps to the side to consume the Sacred Host before moving away from the area in front of the altar.
When receiving Holy Communion on the tongue, the priest elevates the Sacred Host and says “The Body of Christ.” The person receiving Holy Communion responds “Amen” and tilts the head slightly back with the tongue extended over the bottom teeth and touching the bottom lip so that the Sacred Host can be placed on the tongue.
To prepare for worthy reception of this sacrament, the faithful should observe the fast required in their Church. Bodily demeanor (gestures, clothing) ought to convey the respect, solemnity, and joy of this moment when Christ becomes our guest.
[1387, Catechism of the Catholic Church]