Instead of writing a flat sign before every Bb note, it is easier to write the flat sign just once, immediately after the treble clef. This means that all B notes on the staff are played as flats, even though there is no flat sign placed before the individual notes. This is called a Key Signature. See Lesson 15 for more information on key signatures.
Remember to play all B notes as Bb as indicated by the key signature.
This symbol is called common time. It means exactly the same as * .
This song is a duet written in common time. Notice once again the use of a key signature, reminding you to play all B notes as Bb