To do this activity it's expected you understand the content covered in the following:
Play a note on a hidden instrument (e.g. a chime bar), and have a student try to find the note on the piano by guessing the note, and comparing it with the one being played. If the note on the piano is too high, explore the lower half, and vice versa. A kind of binary search can be used to narrow in on the note. You could also do a sequential search - keep playing notes until you hear one that is the same.
This activity relies on student being able to listen to two pitches and work out if one is higher, lower or the same. This can take some experience to be able to do it accurately, and if the timbre of the two sounds is too different, it may be even harder.