The Sacrament of First Communion is an important tradition for Catholic families and individuals. For Catholics, Holy Communion is the third sacrament they receive, and the second of the Sacraments of Initiation. It occurs only after receiving Baptism, and once the person has reached the age of reason (usually, around the second grade). First Reconciliation (the first sacrament of penance) must precede the reception of the Eucharist for the first time as well.

During the Holy Sacrifice of the Mass, when you see priest extend his hands over the bread and wine (and often hear a ring of bells), he is consecrating them and praying to the Holy Spirit that they be turned in the Body and Blood of our Lord. After this moment, we know that the Body and Blood of Jesus is truly present on the altar. 

Every time we receive Jesus in Holy Communion and say "Amen" in response to "The Body of Christ", we are acknowledging that we are receiving the actual body, blood, soul, and divinity of Christ along with everything else the church teaches.