These exercises are a good place to start if you have a rudimentary knowledge of the seven primary modes and the way they're constructed.
If you open the tab labeled 'Ionian' above, you'll see a row of tabs with different note names on each one. You'll be placed on the Ab tab to start and asked to choose the chord for the 2nd degree of the Ab Ionain mode. Select Bb Minor7 (the second diatonic chord in the Ab Ionian mode) from the dropdown list and click the [Submit] button.
The screen will confirm that the chord you chose is indeed the one it expected and you'll notice that the degree changes from the number '2' to a random number between 1 and 7. Now select the chord at that degree of the Ab Ionian mode. If you select a chord other than the expected one, you're prompted to try again.
Good luck and have fun!