Singers learn what different intervals, such as "Do-Re"/"Do-Mi"/"Do-Fa" sound like relative to each other, and then sing the solfege Do/Re/Mi names when you are learning a song (instead of the lyrics), since the relative intervals are the same in every key. This is how choruses, religious congregations, and country singers sight read music is My arrangement of Do Re Mi for the violin is in the key of D Major.To play the song with more ease, I recommend you practice the D Major scale and arpeggio first. zUZGO.