Sometimes a song does not begin on the first beat of a bar. Any notes which come before the first full bar are called lead-in notes. When we use lead-in notes, the last bar is also incomplete. The notes in the lead-in and the notes in the last bar must add up to one full bar.
A black box sitting on the third line of a staff is called a half rest. Sometimes called a minim rest. It means two counts of silence.