Catholics believe that, through the consecration at Mass, the bread and wine become Christ’s Body and Blood. Jesus is truly present—Body, Blood, soul and divinity—while the appearances of bread and wine remain.
A little more context
The Church calls this change transubstantiation. It is more than a reminder or a symbol of an absent Jesus. The Eucharist belongs to the Church’s worship and sacramental life; reverence toward it is directed to Christ himself.
A practical beginning
If this teaching is new to you, begin by reading the Church’s explanation and talking with a parish catechist. You can attend Mass while learning. Participation and receiving Communion are distinct; ask about preparation before receiving.
Source & further reading
USCCB: the Eucharist (opens in a new tab)↗Teaching summaries are introductions. Follow the linked Church source for its fuller context.