The big keyboard on top of the chords calculator acts like a piano keyboard with the help of the mouse.

The left mouse button temporarily strikes a keyboard key.  The key is released as soon as the button is released. As though you had played a piano key with your finger then lifted the finger off the key.

The right mouse button strikes the key, but leaves it down.  The key becomes selected.  As though you play a piano key and leave your finger down.

To release a selected keyboard key, click on it with the left mouse button.  To lift all keys, click on the Clear calculator button:

Try this:

1)  Turn the sound ON (review the previous section if necessary).

2)  Drag the mouse pointer on the keyboard while holding the Left mouse button down

    This is one of the ways to clear the keyboard.  The other is to hit the Clear key

If you do not know a chord name, but you know the piano keys that plays it, then selecting those keys with the right mouse button will display the name of the chord in the calculator.

It does not matter in which octave the four notes are selected, or even if they are in a different order (except the root has to be the same note), for as long as you select the C, E, G and B notes with C at the root, the resulting chord name will be CMa7.