The Mass is the central act of worship in the life of a Catholic.

We go to Mass to spend time with God, and to receive his grace that helps us live a holy, Christian life. The word "mass" comes from the final blessing said by the priest in Latin: "Ite, missa est," meaning “to send out.” This mirrors how Jesus sent out his disciples into the world to share the good news of the gospel.
 

Introductory Rite

The Mass has four basic parts, or "rites." The beginning is called the Introductory Rite. At the beginning, the priest processes in, accompanied by those serving him in the Mass. Often the congregation (all those who are there) will sing a hymn together. Once the priest reaches the sanctuary (the part of the Church where the altar table is), he begins the Mass with the Sign of the Cross: "In the name of the Father, and of the Son and of the Holy Spirit, Amen." This short prayer reminds the people that they are baptised into the One God in three persons, placing themselves under his protection. Then priest takes a few moments to allow the congregation to reflect upon the things they have done or not done which hurt other people, and invites them to ask God for his forgiveness and mercy.

Liturgy of the Word

The second part of the Mass is called the Liturgy of the Word. "Liturgy" is an ancient word which came from the Greeks meaning "official work," making the Mass an official prayer of the Church. In the Liturgy of the Word, everyone listens to readings from the Bible. The first reading is usually a story from the Old Testament, written in the time before Jesus. Then a psalm is prayed or sung on the same theme. The second reading typically comes from a letter in the New Testament, written by the early apostles of Jesus. Lastly, everyone stands to listen to a reading from the Gospel, which shows how Jesus fulfilled the prophesies and promises of the Old Testament. After the readings, everyone sits and listens to the homily, or sermon, preached by the priest. To complete this part of the Mass, everyone recites the Creed (the statement of faith in God) and then prays a set of prayers, called the general intercessions, for local issues and people.

Liturgy of the Eucharist

The third part of the Mass is called the Liturgy of the Eucharist. "Eucharist" means to give thanks, so we begin this part of the Mass by offering ourselves to God. This is symbolised by taking up the bread and wine, which will become the Body and Blood of Jesus Christ, and the collection. During the Eucharistic prayer, everyone kneels in worship of Jesus Christ, who becomes present under the appearance of bread and wine when the priest says the words of the consecration. The change is not "done" by the priest, but by Christ, and whilst there appears to be no visible difference, the change is one of substance, of what it is. Those who are able to receive Holy Communion then process up to receive the sacrament. Those unable to receive Holy Communion, either because they are not Catholics, or because as Catholics they have disobeyed a serious law of the Church and have not been reconciled to the Church, are invited to come forward and receive a blessing, which can be called a spiritual communion.

 

The Catechism on the Eucharist