How do I use this thing?!

There are 2 modes: Practice & Quiz. The practice mode allows you to step through the examples at your own pace. The quiz mode presents a series of questions, then shows you how you did.

Select an interval to work on. Then select a direction.
Select Listen or Sing.
Tap the Play button.

When Listen is selected the app will play both notes of the interval in the selected direction.
Tap the Repeat button hear the notes again.
Tap the Play button again to hear another pair of notes.

When Sing is selected the app will play the first note, and you provide the second.
Tap the Record button and sing the note. The app will tell you if you got it right or not.
If you're stumped, tap the Next button to hear the second note.
Tap the Repeat button to hear the first note again.
Or tap the Play button again to hear a new note.

Each quiz is 10 questions.
The quiz defaults to all intervals. If you want to work on a specific subset of intervals, tap the gear icon and deselect the intervals you want to leave out of the quiz.
Select either Listen or Sing.
Tap New. The quiz will start. After each response the app will automatically advance to the next quiz item.

Your results will be displayed at the end.