The fretboard of the guitar is the point where the keys are cut, able to play the various musical notes just like a piano keyboard.
Usually have 21/22 keys keyboard, but there are keyboards of 24 or even 26 keys!
So according to the chromatic scale, the first key of the first string (the thicker, the low-MI) have an F, up to the twelfth fret that I resumed the open string with an octave higher.
Then on the twelfth fret the notes repeat all of the first part of the neck, an octave higher. Continuing we have that in the twenty-fourth button then you will have the same notes an octave higher still.
If your guitar is tuned in the standard version (EAGDBE), the arrangement of notes is as follows: (see pics above).
If you use special tuning (half step down, drop D, drop B, etc. ..) the disposition of the notes will change accordingly!
One piece of advice you give to everyone is to use a finger for each button! Having five fingers (hopefully!) and using the thumb as a "hook" on the handle, the palm can cover our four keys at a time without making unnatural movements of the fingers and without bending.
The finger that suffers most from this technique is certainly the little finger, a mixed blessing for all guitarists!