The app serves to select / set a scale that you can watch as a reminder when making music. By default, it is set to C major, which contains the 7 white notes on the keyboard. These are indicated with green in the main screen because they are in that scale.
At the top left are 2 buttons: “Major” and “Minor”, which you can use to switch between a major, minor and a custom scale
Additional settings must be made for the adjusted scale.

Below “Major” and “Minor” there are 12 buttons with which you can select the start note or key of the desired scale.

On the keyboard below you will see the notes in the set scale with a green overlap.
The first note of the set scale is always indicated with number 1.
You can play the notes by pressing them. This can also be done through the computer keyboard or with a connected gamepad.
Under the piano keyboard on the screen are buttons with the number of possible chords in the set scale.
By pressing on them, the 1st, 3rd, 5th and possibly 7th note is indicated in red. The possible indication of the 7th note is a setting in the settings screen.
Higher notes are lowered one octave, in the app only 1 octave is displayed visually.

On the screenshot above, the major D # scale is set and the button with 1 is pressed for the first chord. Next to the chords buttons, at the bottom right, the type of chord then appears: “Major”, “Minor” or “Dim” for a diminished chord.

It is possible to operate the entire application with just a computer keyboard or with just a gamepad.
The gamepad buttons correspond to Xbox and Playstation controllers, therefore there are pictures of both types of controllers.
One can navigate with the arrows, a light blue selection indication is shown around the selected button.
Here, for example, the C # button is selected: 
Spacebar or enter to press the selected button.
You can also do this with the gamepad’s arrows and the A button to confirm. If you press an arrow you go into navigation mode.

When you want to close a screen or popup, or you want to go out of navigation mode, you can do the cancel action (B button with gamepad, “escape” key with keyboard)
The notes of the keyboard on the screen are linked to gamepad and computer keyboard buttons when on the main screen and not in navigation mode.

Normal minor and major scales have 7 notes.
these are connected with the following keys and buttons:

L2 for the first note, L1 for the 2nd, R1 for the 3rd, R2 for the 4th, X for the 5th, A for the 6th, B for the 7th
and the keyboard keys “s”, “d”, “f”, “g”, “h”, “j”, “k” which are next to each other on qwerty and azerty keyboards.

“s” for the first note in the scale and then to the right.
However, it is also possible to play the notes always with the same keys by setting the “Notes remap” switch to “OFF”.

L2 of a gamepad and the “s” key of a keyboard are then always on the C note, gamepad L1 and “d” on the D note, gamepad R1 and “f” on the E note, gamepad R2 and “g” on the F note, gamepad X and “h” keyboard on the G note, gamepad A and “j” keyboard on the A note, gamepad B and “k” keyboard on the B note.

For the black keys, the keys above it can be used on a computer keyboard: “e” for the C # note, “r” for the D # note, “y” for the F # note, “u” for the G # note and “i” for the A # note.

With a gamepad, a note can be moved down or up with the left stick.
e.g. L2 + stick upwards gives C #

As long as the All note switch is set to “OFF”, only the notes marked with green in the set scale can be played. However, if you want to play all notes, you can set the “All notes” switch to “On”.With this setting, the “Notes remap” switch will always jump to “OFF”.

There are several additional settings possible, you can get there trough the pancake button.