When FastChords starts the chords calculator and the keyboard appear on the screen.  The keyboard is sometimes referred to as the "big keyboard" to differentiate from the small keyboards that appear in the chords table.

Because the chords calculator is visible, the program is in "Chords Mode", that means you can enter chords.   The other three  possibilities are "Table Mode", the "Melody Mode" and the "Player Mode".

The buttons in the chord calculator are divided into two groups:  group 1 deals with chord symbols and group 2 with operations such as saving chords to the chords table, clearing the keyboard and turning sound on or off.  The buttons for the first group appear at the bottom of the calculator window, those for the second at the top.