Here is the note B on the treble staff and the bass staff.
In Lesson 7 this B note was written on the treble staff and you played it with your right hand. In this lesson the B note is written on the bass staff and you play it with your left hand thumb.
The next song contains first and second endings. The first time you play through the song play the first ending, Z then go back to the beginning. The second time you play through the song, play the second ending X instead of the first.
In the Butterfly Waltz, play through to the end of the first ending (bar 8), then repeat the song from the beginning as indicated by the repeat dots. when you play through the song the second time, do not play bars 7 and 8 again (the first ending), but play bars 9 and 10 (the second ending).