An interval will sound, either melodically or with both notes heard together. Touch the name of the interval you think you heard. To hear the interval again press the triangular "Play" button at the top center of the screen.
The program will gradually work through various contrasting pairs until you show mastery of their differences. After you've shown success with each distinction you'll be asked to choose your answer from a larger group of intervals.
If you make a mistake the program will display both choices on the staff, with your choice below the correct one. You can use the "Hear your choice" button to compare the two.
To enter Practice Mode touch "Practice" at the top of the screen. Points are not counted in practice mode and you can choose particular intervals for practice. You can also choose whether you want to hear the intervals melodically (ascending or descending) or harmonically. To bring up the practice window again touch "Change practice choices" above the selection boxes. To leave practice mode touch "Exit Practice" at the top of the screen.