A tie is a curved line joining two or more notes of the same pitch. The first note is sung, and is then held for the value of the extra note (or notes). The initial note is sung for the value of all the tied notes.
Sing the note G in this example and sustain it for six beats.
A tie is the only way of indicating that a note is to be held across a bar line (as shown previously). It is also way of increasing the length of a note within a bar.
Do not confuse the tie with the slur, which connects two notes of different pitches.