Now let's take a look at how the notes are represented and placed on different instruments. First we look at he piano, because it is the most intuitive instrument to understand the notes. That's because it lays out all notes in a single line, just like they are positioned in the musical alphabet.
All natural notes have white keys, and the accidental notes are put in between as black keys, where we have a full-step between the natural notes. The piano has a total of 88 keys, but let's look at the first 13 keys first.
Like in the musical alphabet, the notes are ordered from A to G, and then start over again with A. Then the pattern is repeating until we have all 88 keys. As keys are repeating, they become higher in pitch, and therefore have a higher frequency. This is referred to as octave, as discussed in the notes chapter. The A in the next octave has exactly double the frequency of the A below it, and sounds the same, just higher, so we say it's an octave higher.
Looking at the guitar, each string is tuned to particular note when it is strummed without pressing it against any of the frets. We call that an open string. Starting with that open string note, it then lays out the notes in order, each fret a semitone or halt-step above the previous one. Here we see the E string, the open string note is E, the first fret is F, the second fret is F♯, and so on. We are still following the note order of the musical alphabet, but start at a different point.
Each string is tuned to a different note. The lowest string is tuned to E, and the highest string is tuned to E as well, but an octave higher. The strings are tuned in a way that makes it easy to play chords and scales, which makes things not as simple and linear as on the piano. A typical guitar has a total of 22 frets, but let's look at the first 12 frets first. On each string, once we reach the end end of the musical alphabet relative to the starting note, we simply start over again. On the 12th fret, the note of the open string is repeated, but an octave higher.
The layout also means that the exact same note can appear multiple times on the fret board, and can be played on different strings, and at different frets. This is very different from the piano, where each note only appears once. This is why guitar players often refer to the fretboard as a 'grid', because it has a more complex layout than the piano.