Barring dispensation from the local bishop (e.g., in the current situation of pandemic), Catholics are required to attend Mass every Saturday evening or Sunday and on Holy Days of Obligation, under pain of mortal sin (if one is absent without just cause).  Justified absence may include (among other reasons) illness, illness of a family member, being homebound, lack of transport, inability to attend a local mass while traveling, or unavoidable work (e.g. doctors, nurses, LEOs, EMTs, etc.) due to public service or family support obligations. 

Canon Law provides for a pastor to dispense an individual  from the Obligation "for a just cause and according to the prescripts of the diocesan bishop... or can grant a commutation of the obligation into other pious works." 

"When the Mass is being celebrated, the sanctuary is filled with countless angels, who adore the Divine Victim immolated on the altar."

St. John Chrysostom

1. Procession 
2. Acknowleding Sins
3. Glory to God

1. First Reading
2. Responsorial Psalm
3. Second Reading
4. Gospel Acclimation
5. Gospel
6. Homily
7. Profession of Faith
8. Petitions
9. Offeratory

1. Sanctus (Holy, Holy, Holy)
2. Eucharistic Prayer 
3. Consecration
4. Great Amen
5. Lord's Prayer
6. Kiss of Peace
7. Agnus Dei (Lamb of God)
8. Holy Communion
9. Rest
10. Final Blessing
11. Dismissal

Introductory Rite

1. Procession - The priest, deacon, and altar servers enter the church.  The deacon carries with him the book of the Gospels, of which, by virtue of his office, he is the ordinary custodian.  Sacred music accompanies.  
2. Acknowledging Our Sins - The priest calls upon the faithful to humbly consider the state of their soul and personal failing before God.  He, along with the faithful, invokes the Confiteor ("I confess ...") and the Kyrie.   Or, the deacon invokes the three trophes ("You were sent to heal the contrite of heart...etc.")
3. Glory to God - Having expressed regret for our sins, it is now appropriate to give glory to the Father, ordinarily in uplifting song.  

1. First Reading - The first reading is typically an excerpt from the Old Testament, although during Easter, it is typically a reading from the Acts of the Apostles.  
2. Responsorial Psalm - The psalms are the ordinary repository of prayer that the Church invokes throughout the day in not only the Divine Office, but at every Mass.  The faithful repeat the refrain, and reflect on the verses.
3. Second Reading -  The second reading is typically an excerpt from the Catholic epistles in the New Testament (Paul, James, Jude, Peter, John, etc.)
4. Gospel Acclimation - During ordinary time and Advent, the "Alleluia" is sung (never spoken).  During Lent, it is not appropriate to sing "Alleluia" and so another acclimation is substituted, simply praising Christ.  
5. The Gospel  - The Gospel is ordinarily read by the Deacon or Priest, but never by the laity.
6. The Homily - The Homily is presented by a deacon or priest (never the laity).  A layperson (or religious) may be invited to give commentary or a presentation only after the deacon or priest comments on the day's readings.  A homily is not a sermon.  A sermon gives general instruction, but does not pertain to the readings proper to the Mass of the day. Sermons more properly refer to non-Catholic denominations.
7. Profession of Faith - As individuals in one body, we declare our assent to the Catholic faith as taught from the beginning. 
8. Petitions - The needs of the people are brought to God, to be offered with the priestly sacrifice during the Liturgy of the Eucharist.
9. Offeratory - The faithful supply the bread and wine to be transubstantiated into the body and blood of Christ.  The priest presents these humble offering to God, that He might find them worthy, not unlike Abel bringing the choice lamb in Genesis.  

1. Sanctus (Holy, Holy, Holy) - The veil between heaven and earth is pulled back as we give praise with the angels before God.  
2. Epiclesis - The Eucharistic prayer begins with the calling down of the Holy Spirit to bless the bread and wine before it is consecrated.  The priest holds his adjoined hands just above the offering, and a brief ringing of the altar bells calls attention.
3. Consecration of the Bread and Wine - The priest utters the words that will confect the Body and Blood of Christ in what was the bread and wine brought to the altar by the people.  It is no longer bread and wine:  it is now "the Host (or Body)" and "the Precious Blood" of Christ.  The appearance and sensibility of bread and wine remain, but the substance has miraculously changed.  This is called transubstantiation. 
4. Great Amen (the elevation) - At the end of the Eucharistic prayer, the priest elevates the Body and Blood (or, a deacon, if present, elevates the Blood) as a re-presentation of the crucified Christ to the Father in heaven.
5. The Lord's Prayer - With confidence that God has found this a worthy sacrifice, we pray to the Father in the words that Jesus taught us.  The "Our Father" is a prayer of praise, petition, and repentance for our sins at the moment He is most appeased by the Sacrifice of His Son.
6. Kiss of Peace - The people of Christ are exhorted to approach the altar without harboring animosity for their neighbor, and so a symbolic exchange of peace occurs.
7. Agnus Dei (Lamb of God) - Echoing the words of John the Baptist, we proclaim that Jesus Christ is the Lamb, Who, by His Sacrifice, takes away the sin of the world.  At this time, the priest breaks the Host, mirroring the Passover sacrifice of a lamb that is first broken, then consumed, except in this case, Jesus is the Lamb, and the sacrifice is upon the Cross.  
8. Completing the Sacrifice -The priest then consumes the Host and the Precious Blood.  THIS IS ABSOLUTELY NECESSARY FOR THE MASS TO BE CONSIDERED VALID.  If a priest does not consume both the body and blood, the sacrifice has not been effected (i.e., the Mass is invalid).  This again mirrors the Passover sacrifice which requires the Lamb to be consumed after it is sacrificed.  
9. Holy Communion - After the deacon receives the Body and Blood, the people are called forward to participate in consuming the sacrifice which they have assisted in. Returning to our pews, we properly take the time to give thanks for the gift of the Lord. It is not the time for petitions or repentance, but to offer thanksgiving (which is the meaning of the word "Eucharist")
10. Rest - Reflecting the reality of the new "Sabbath" -- the Lord's Day -- we "rest" and reflect on the magnitude of what God has done.
11. The Sending Forth - With a final blessing from the priest, the people are exhorted to go outside the doors and bring with them the grace they have received in Word and Sacrament, to evangelize and emulate the very Lord they have within them.