So far, you have sung the names of the notes (C and D) and the sound "la" for each song in the book. When you say or sing a single sound like "la" it is called a syllable. All words are made up of syllables. For example, the name Mary contains two syllables: Ma-ry.
There are particular syllables which can help you learn to sing and hear the difference between different pitches. These are called sol-fa syllables. Each syllable matches a different musical pitch.
The sounds of these syllables are do, re, mi, fa, so, la, and ti. They are a bit like the musical alphabet, because each syllable goes with a different note. The first syllables we will learn are do (Pronounced "doe") and re (Pronounced "ray"). Do is C and re is D.
As you go through this song, sing do for every C note and re for every D note.