First Holy Communion

The holy Eucharist completes Christian initiation.  Those who have been raised to the dignity of the royal presthood by Baptism and configured more deeply to Christ by confirmation participate with the whole community in the Lord's own sacrifice by means of the Eucharist.(1322 Catechism of the Catholic Church)

"At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood.  This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquest 'in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us.'"(1323 Catechism of the Catholic Church)

Then He took the bread, said the blessing, broke it,
and gave it to them, saying, This is my body,
which will be given for you; do this in memory of me.
And likewise the cup after they had eaten, saying,
This cup is the new covenant in my blood, which will be shed for you.
Luke 22:19

The faithful are to receive the Eucharist at least once a year. Those who receive the Eucharist are to abstain from any food or drink, with the exception of water or medicine, for at least one hour before Holy Communion.

A person who is conscious of grave sin is not to receive the Body and Blood of the Lord until they have celebrated the Sacrament of Reconciliation.  If it is not possible to do so, the person may receive the Eucharist, with the intention to celebrate Reconciliation as soon as possible.