The Mass on Holy Saturday is the Easter Vigil, though its full reference on the USCCB schedule of daily reading is “Easter Sunday The Resurrection of the Lord Holy Saturday At the Easter Vigil in the Holy Night of Easter.”
This is the most unique and perhaps most important liturgy of the year. The Easter Vigil ends the Triduum and begins Easter celebrations.
The service can only begin once the sun has set. Outside the church, a fire lights the Paschal candle, and the flame is shared throughout the church to individual handheld candles. The Liturgy of the Word, which normally includes nine readings, begins in darkness.
The readings demonstrate the connection between the Old and New Testaments and how Jesus fulfilled Scripture and achieved salvation for all humanity.
The Liturgy of Baptism, which follows the Gospel and homily, marks the culmination of the Rite of Christian Initiation of Adults (RCIA) program. Catechumens, who have been preparing to enter the Church, are baptized, confirmed, and later receive their first Holy Communion.
The Easter Vigil is a joyous, celebratory liturgy, filled with rich songs. Although the services ends late at night, churches typically have a reception afterward to continue the celebration.
https://bible.usccb.org/bible/readings/040823.cfm