There are various musical items in a Choral Evensong service. These are, typically:
Introit; Preces; Psalm; Magnificat; Nunc Dimittis; Responses; Anthem; Hymn(s); Organ Voluntary.
The links below (highlighted in red) demonstrate some of the greatest manifestations of these musical forms.
And here is a Gramophone article listing some choice recordings of the Choral Evensong repertoire - by Michael White
These are short petitions that are sung alternately as versicle (by the precentor) and response (by the choir, and sometimes congregation). This form of prayer is one of the oldest in Christianity, finding its source in the pre-Christian Hebrew prayers of the Psalms in Temple Worship. The 'Preces' and 'Responses' are separated within the Evensong service, with the Psalm, Magnificat and Nunc Dimittis happening in between them (see order of service above).
Smith - Preces and Responses
The Old Testament Judaic book of 150 songs of praise, lamentation and thanksgiving - many of which are linked to King David.
This is the joyful song of praise by the young woman, Mary, rejoicing at the prospect of the birth of her child, Jesus.
This is the song of an old man, Simeon, praying to God to let him depart in peace now his life has been fulfilled by meeting Jesus.
This is a choral composition set either to a text from the Bible, or another religious text.