Look over the sheet music. Note that there are only four staves, as opposed to the modern tradition of five. Keep in mind that there is no time signature or key signature. Observe that the neumes, which are the square notes, go up and down to indicate the rising or falling of vocal pitch.
Keep the solfege syllables in mind when reading neumes. The solfege scale, spanning an octave, is as follows: do, re, mi, fa, sol, la, ti, do. Do is considered the starting point, and is movable. A pitch pipe can help you check your accuracy as you are learning a new piece.
Note that the Gregorian scale has two half steps, with the remainder functioning as whole steps. The half steps fall between solfege syllables ti and do and between mi and fa.
The C-shaped clef marking at the beginning of the music indicates where do is. The fa clef orients the singer to the fa, and appears as a "C" with a backward lower case "r" back to back with one another.
Understand the rhythm indicated by neumes; refer to the diagram to reference the appearance of neumes. The punctum has a pulse for a single syllable; the podatus has one pulse on two notes, where the lower note is sung first on one or two syllables; the clivis has two notes, each with one pulse, on a single syllable in which the top note is sung first; the torculus is three notes with one pulse each sung on a single syllable; the porrectus is three notes with three pulses on a single syllable (see Resources).
Observe the notation. The only accidental found in chant notation is the flat, which lowers ti by one half step, creating te. A dotted note is an indicator to hold for two pulses, and a note with a line, or episema, over it are held slightly longer.
The flexus is a descending line connecting two notes that indicates a descending pitch. The resupini, praepunctis and subpunctis are diamond-shaped markings that follow ascending notes and indicate a complementary descent in pitch.