The document outlines the structure and key elements of the Mass of Paul VI, which was introduced in 1969 and replaced the previous Tridentine Mass. It describes the Mass as being divided into three main parts: the Introductory Rites, Liturgy of the Word, and Liturgy of the Eucharist. Each part includes specific prayers, readings, and rituals such as the opening song, first and second readings, homily, Eucharistic prayer, and communion.