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. Do not confuse the tie with the slur which connects notes with different position on the staff and indicates legato.
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).