The tie is a curved line that connects two notes with the same position on the staff. A tie tells you to play the first note only, and to hold it for the length of both notes.
Play the C note and hold it for six beats.
In this song there are ties between bars 3 and 4, and between bars 7 and 8.
In this song, a tie is used between bars 15 and 16 (two E notes), and between bars 31 and 32 (two F notes).