The Sacrament of Eucharist is one of the 3 Sacraments of Initiation.
The Eucharist is the source and summit of Christian life. It is a celebration, a thanksgiving, and an act of adoration and to glorify God. The Mass is the divine act of God reaching out to make us holy and our response to him in our active participation during Mass. It is both a sacrifice and a Sacrament.
Jesus nourishes our body with his Flesh and Blood. In John Chapter 6, many of his disciples left him after he insisted that they need to eat his flesh and drink his blood to have eternal life. "This is hard teaching, who can accept it?" (John 6:60)
Jesus died only once at Calvary but because of its mystery, the sacrifice is prolonged through the ages and so we make Jesus re-present again everytime we celebrate the Eucharist.
The Mass is divided into two parts: Liturgy of the Word and Liturgy of the Eucharist.
The graces (supernatural gifts) of Holy Communion are 1) it unites us to the Lord, 2) it nourishes our spiritual life and gives us what we need to grow spiritually, 3) it cleanses us from past sins, 4) it strengthens the bonds of Christian love within us, 5) it makes it harder to fall into mortal sin in the future and 6) it reinforces the unity of the Church as the Body of Christ.
The matter (visible sign) are: bread and wine.
The form (words) are: "This is my Body.... this is my Blood..."