In this exercise, Solfege will display one or more intervals, and you should sing them. Unfortunately, it is not yet possible to sing into a microphone and let Solfege decide if you sing correct, so you have to decide yourself if you are correct or wrong.
The program will try to make a question where all tones are within the range the user can sing, as configured in the preferences window. Sometimes, it is not possible to keep the question within this range, for example when the exercise is configured to create many intervals where all intervals go upwards.