The first responses to learn
Begin with Amen, Lord have mercy, Alleluia, and the sign of the cross when the people make it. These responses appear often and give you natural places to participate.
It also helps to learn the meaning before the sound. Amen receives the prayer. Lord have mercy asks for God’s compassion. Alleluia gives praise. The sign of the cross confesses the Holy Trinity and Christ’s saving Cross.
A practical rule
When you are unsure, listen. When a response repeats and you know the meaning, join softly. When the service moves quickly, return to prayer in your heart.
Over time, the repeated responses become a map of the service. They teach when the Church is receiving a blessing, asking for mercy, praising God, confessing faith, or preparing for Communion.
If you want one concrete starting point, learn “Lord, have mercy” and “Amen” first. Those two responses appear throughout the service and give you a steady way to pray even while the rest of the hymnody is still unfamiliar.
Then add Alleluia and the short Coptic mercy responses as they become familiar.