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 (or pick-up notes). When we use lead-in notes, the last bar is also incomplete. The notes in the lead-in and the notes (or rests) in the last bar add up to one full bar. When playing songs with a lead-in, do not press the chord key until the first beat of the first full bar.
On the recording there are five drumbeats to introduce this song.
A black box sitting on the middle line of the staff is called a half rest. Sometimes called a minim rest. It means two beats of silence.