What are the two main parts of church mass?

Roman Catholic Answer

The Liturgy of the Word, and the Liturgy of the Eucharist; or, as they were know before Vatican II, the Mass of the Catechumens and the Mass of the Faithful. The first part ends after the homily and creed, and the second part starts with the Offering of the Gifts.
There are two main parts of the Mass, before 1962 they were known as the Mass of the Catechumens and the Mass of the Faithful. Now the first part is known as the Liturgy of the Word, and the second part is known as the Liturgy of the Eucharist. The Liturgy of the Word runs up through the sermon and the intercessions. Then the Mass moves to the altar and the second part continues with the Offering of the Gifts.
The first part is the Mass of the Catechumens, as it was called before the Second Vatican Council, and is now split into two pieces: the Introductory Rites, which lasts from the Priests entrance until the conclusion of the Opening Prayer following the Gloria, and the Liturgy of the Word which lasts from the first reading until the General Intercessions.

The second part of the Mass is the Liturgy of the Eucharist, also called the Mass of the Faithful prior to the Second Vatican Council, which lasts from the Presentation of the Gifts until the Dismissal.
In brief, there are three main parts:

The Introductory Rites
The Liturgy of the Word
The Liturgy of the Eucharist

In the Introductory Rites, we prepare ourselves for the Sacrifice of the Mass by Praising God, (opening hymn) Making the Sign of the cross (Everything we do is Trinitarian) and acknowledging our sins (We say together the "I confess"). We ask God for his mercy (Kyrie Eleison, or Lord have mercy) and then usually say or sing the "Glory to God", which recalls the song of the angels at the birth of Jesus. Following the opening prayer we move onto the

Liturgy of the Word - where we meet Christ in the scriptures., Usually, a passage of the Old Testament, then a psalm with its response, then a passage from the New Testament (letter of St Paul to the Church, usually) and then the Alleluia (except in Lent) and the Gospel . This is followed by the homily, where the priest explains the scriptures (usually the Gospel) and how we can put it into practice,. This is followed by the Creed, and then the Bidding Prayers (where we pray for the Church and the world).

The Liturgy of the Eucharist follows. (this needs a whole section by itself, but briefly includes the prayers of Offeringl whereby bread and wine are blessed and offered, and God is thanked for his goodness and provision. The Holy SPirit is invoked, to change them into the body and blkood of Christ, and the words of the Last Supper are said "This is my body, this is my blood". We recall that Jesus died for our sins when we say "Lamb of God". And finally the priest, then the people, receive the body and blood of Christ.;
The Liturgy of the Word and The Liturgy of the Eucharist.
The Liturgy of the Word and the Liturgy of the Eucharist. During the Liturgy of the Word (the first half or so) the readings and the Gospel are read aloud, and the homily is delivered. During the Liturgy of the Eucharist, the bread and wine are consecrated into the Body and Blood of Christ, Communion is given, and the Final Blessing on the congregation is said.
The various parts of a Catholic mass are as follows:

1) Pre-Mass devotions
2) Introductory rites
3) Liturgy of the Word
4) Liturgy of the Eucharist
5) Communion rite
6) Concluding rite


Another answer
The Catholic Mass is generally divided into two large segments: the Mass of the Catechumens; and the Mass of the Faithful.

The Mass of the Faithful consists of an introductory rite, a penitential rite, the recitation of the Kyrie, on Sundays and major feasts the recitation of the Gloria, and then the collect/prayer of the day.

The Liturgy of the Word is carried out during this part of the mass, it directly follows the Opening Prayer of the day. There are three readings and a psalm on Sundays and major feasts, and two readings and a psalm on weekdays. The gospel follows, directly preceded by the recitation of the Alleluia (proper for the day).

After the gospel the Priest delivers the homily, and the congregation recites the Creed (on Sundays and major feasts).

At this point, the Mass of the faithful begins. It consists of the offertory rites, offertory procession where the gifts are presented to the priest. Then begins the Canon, the Eucharistic prayer, beginning with a proper preface, followed by the recitation of the Sanctus (holy, holy holy...). In the midst of this, the priest begins the institution narrative (The night before he was given up to death he took bread...). This is the point where Transubstantiation occurs.

The Eucharistic prayer ends with the doxology (through him, with him, in him...) and the great Amen. After this the Communion Rite begins. Here is recited the Lord's Prayer ("Our Father"), the fraction of the host, and the reception of holy communion. And finally after all that has been done, the priest dismisses the people. "The mass is ended, Go in peace to love and serve the Lord."