The difference is that while tapping out the beats, you're supposed to sing a note—any note—on the beats that have the line over them, and not sing on the beats that don't. You're supposed to sing a single note, and that note is supposed to last the length of the beats that have the line above them.
In other words, you tap or clap out a steady beat, and for exercise (a), you sing a note lasting five beats, then don't sing for five beats, then sing another note lasting five beats, then don't sing for five beats, etc.
For exercise (b), you sing a note for the first four beats, then don't sing for four beats, then sing for four beats, then don't sing for four beats. etc.
And so on. For these exercise, at least, you don't need an instrument of any kind, including the virtual piano. These exercises are about training your ear and sense of rhythm; the actual notes aren't important.