A sharp, flat or natural sign written immediately before a note, (not at the start of aline) is called an accidental.
In this riff, accidentals are used to indicate that there are two Bb notes and one B@ in each bar.
This blues contains sharps, flats and naturals.
This song is a 12 bar blues. It contains sharp, flat and natural signs.
The symbol ? in bar 14 is called a pause or fermata. It means that you can sustain the note for as long as you wish.
You can now play the song Santa Lucia, on page 36 of Supplementary Songbook B.