Middle C (that’s button C3 on the press) is notated as  C
The D immediately above middle C is notated as D
The E above that is notated as E
And so on up the scale.

Starting at middle C, the notes in that octave are shown as    C D E F G A B

The next note up is a C again – but to show it is in the higher octave, that C is shown in lowercase as  c
So a full one-octave C major scale from middle C is –   C D E F G A B c

So going from middle C to the B one octave and 7 notes above that is – C D E F G A B c d e f g a b

And we’re back at yet another C note. The next octave up is shown by an apostrophe immediately after the note name, like – c’

So our scale now runs two octaves from middle C:      C D E F G A B c d e f g a b c’

And using the apostrophe to denote the upper octave we can extend our scale further :

C D E F G A B c d e f g a b c’ d’ e’ f’ g’ a’ b’

But what about the B immediately below middle C ?

That octave is shown by a comma immediately following the note name, e.g.  B,

We now have four octaves at our disposal, which is more than enough for our purposes of notating traditional music:

C, D, E, F, G ,A, B, C D E F G A B c d e f g a b c’ d’ e’ f’ g’ a’ b’