Sometimes a piece does not begin on the first beat of the bar. Any notes which come before the first full bar are called lead-in notes (or pick-up notes). When lead-in notes are used, the last bar is also incomplete. The notes in the lead-in and the notes in the last bar add up to one full bar. When you are playing chords do not strum until the first full bar, after the lead-in notes.
The next melody contains first and second endings. The first time you play through the song, play the first ending, (Z), then go back to the beginning. The second time you play through the song, play the second ending (X) instead of the first.
In the following melody "The William Tell Overture", play the first eight bars, then repeat from the beginning but don’t play bar 8 the second time through, but instead go to bar 9.
This melody also begins on the fourth beat of a bar with two lead-in notes. This melody also has only three beats in the last bar because the last three beats the two lead-in notes at the beginning of the song add up to one complete bar (i.e., 4 beats).