Look at No. 1 in Schumann's Album for the Young--be sure it's the Henle edition. Is there anything you don't understand?

"What is that hairpin in measure 5?"

It means you should listen for what happens to the quarter note when the left hand's eighth notes move within it. It means that in all probability you played the first four bars too fast to notice that all those off-beat eighth notes actually make a difference in the sound of the melody. In fact, it may be the reason why Schumann has not given a tempo indication for this piece: the hairpin is the indication.

Do you know of other markings that show what to listen for rather than what to do?