Using Harpninja

Ive been using Harpninja for some time and find it great for learning to bend.  I can see there is a lot more to this than simply doing bends.  I watched the tutorials and still came away confused.

Im an intermediate player so I still spend nearly all my time in second postion.  So that obviously means if Im on my A harp second postion Im in the key of E.  So I set Harp Key to A and display Key to E and display scale ot Mixolydian.  

Questions include

- What do I do with Display Chord on the Settings screen?

- When I see the chord buttons at the top of the Harmonica scree I expected to press 1 (1 chord?).  In the key of E the one chord should be E F# G# but the those buttons dont light when I press A 1.  

- The 7 bottons at the top of the Harmonica screen labeled A 1 to 7d etc.  I clearly dont know what they are.

Im clearly confused.  Can anyone point me in the right direction and how to use this feature or other features of Harp Ninja for practice.  How do you use it?