Click on the menu word "Compose" and select "Show Tips" to allow a square balloon to appear, showing the appropriate data for wherever the mouse cursor is hovering over the Musical Pieces window.
"Show Tips" is a very useful feature, particularly when first learning how to use Tonescape to compose. Below is an example (except, unfortunately, the mouse cursor was not captured by the screen-shot):
If "Show Tips" gets annoying (which it probably will), just turn it off and on as desired.