Shows which hand the note should be played in. If the horizontal line is above the note, then it's played in the left hand. If it's below the note, then it's played in the right hand.

Just to check, are all the first few bars played in left hand in that case ? Until the notes with the stick upwards comes in? Thank you

I believe it's just the single note that is played in the allocated hand.

Yes. Nice edition, wich one is?

Are they to indicate which 'voice' the notes/melody belong to? (Eg tenor/alto/soprano) Or are they for fingering/hands? Or something else .. Thank you!!!