This is not so much for the musician. The average church musician already knows what I'm writing below. This is for the "Average Joe" in the pew who knows nothing of this sort, except (hopefully) to sing with the congregation.
This is the short ditty I let the choir sing just before Mass begins. By right, it should be done at the entrance procession of the celebrant and ministers, but since American Catholic culture has a thing for using hymns at this place, instead of the Proper for Mass, I let the choir do it here. I don't do it at Masses where I'm by myself.
First is the place where the hymn is sung (Processional, Offertory, Communion, Recessional). Next is one of two things - either the TUNE NAME (deliberately printed in caps) that the tune is sung to or the composer name (printed in lower case) that wrote the music. Then it's the first line or common title of the hymn text (lyric), followed by the number in the missalette or music issue, where applicable.
In the case of some tunes which are chant, you may see, in place of the TUNE or composer name, a Mode - e.g., Mode V, Mode I, Mode VII, etc. That means the chant tune was written in one of eight Modes commonly used in Gregorian chant. This has to do far more with what the "tonic" or "first" note of the scale used in a particular piece than it does the melody itself.
Mass settings (Ordinary/Proper):
These be the Introit (see above), the Kyrie (Lord have mercy), Gloria (Glory to God), Psalm (following the First Reading), Alleluia (before the Gospel), Sanctus (Holy), Mysterium (or "Memorial Acclamation"), Per Ipsum (Amen), Lord's Prayer, Agnus Dei (Lamb of God), and Communion Proper (like the Introit, it's only sung at choir Masses, after Father's done purifying the Chalice). The composer name is listed, as is the Mass setting (e.g. Peloquin - Mass of the Bells). In the case of some of the listings, you may see "Tone 8" or "Tone 2", etc. This means one of the eight Gregorian Psalm tones, in simple form, is being sung.
A Mass setting marked with a Roman Numeral is one of the Latin Chant Masses from the Kyriale. Chances are, the Sanctus and Agnus Dei settings in Latin at Holy Ghost will be from Mass XVIII, which has a couple of names - "Missa Pro Defunctis" (Mass for the Dead) or "Missa Pro Feriae Adventi et Quadragesimae" (Mass for Weekdays of Advent and Lent). These two commonly used, yet very simple, chant settings are also compiled in a 1974 collection by the Vatican, called "Jubilate Deo" (Be Joyful to God), a collection of the simplest chant Mass ordinaries that could be easily sung by the average congregation, and not just the choir.
This post, hopefully, will be of help particularly to any parishioners of Holy Ghost who may be interested in knowing in advance what will be sung on a given Sunday, so that they may understand these listings better.