The celebrant stands at the midst of the altar, facing it, and sings (or speaks) the Kyrie with the congregation.
The Latin rite continued to sing the Kyrie in Greek. Historically, this is one of only two places where Greek has been retained in the Latin rite. The other is the use of Greek and Latin at the Tres Hagion in the Good Friday liturgy.
We are accustomed to singing the Kyrie in a three-fold manner. It may also be sung in a nine-fold manner. In this form, the "Lord, have mercy...," is sung three times; "Christ, have mercy..., three times; and "Lord, have mercy...," three times.
If sung or spoken in either the three-fold or nine-fold manner, the petitions may be sung in alternation with the celebrant.
The Gloria in Excelsis is also intoned by the celebrant at the midst of the altar.
The Gloria, the Creed and the Sanctus enjoy equal status in the liturgy. When Mass is celebrated with the assistance of a deacon and sub-deacon, the rubrics indicate that these ministers move to stand beside the celebrant at the altar when they are sung. At all other times these ministers remain in their appointed places.
The historic rite indicates that the Gloria in Excelsis is to be sung at all Masses, excluding only those which are celebrated in violet or black vestments.