Staff: A set of 5 horizontal lines where each line and each space between the lines represents the ‘natural’ notes of the western heptatonic scale (7-note scale).
It is essentially designed around the C major scale (and its related modes).
System: One line of a group of staves.
Below, two staves (plural of staff) are shown together. The staves are grouped by bar lines running through both staves and a bracket at the left. This particular pair of staves is called the grand staff and is used for piano and choral music to show a wider pitch range than a single staff can (efficiently) show.
Treble Clef or ‘G’ Clef:
The symbol was originally the letter ‘G’ and was gradually stylised into the current symbol. The bottom half of the circle encloses the note ‘G’.
A popular mnemonic device for the notes of the lines of the treble clef is, from low to high, “Every Good Boy Deserves Fudge” (or “Even George Bush Deserves Fudge”). The notes of the spaces of the treble clef spells “F–A–C–E”
Bass Clef or ‘F’ Clef’
The symbol for the bass clef was originally the letter ‘F’, which was gradually stylized into the current symbol. The two dots are the remains of the two horizontal lines of the letter ‘F’. They enclose the note ‘F’.
From the clef, it is easy to figure out the note names for each line and space of the staff.
For the bass clef, a mnemonic device for the lines is “Good Boys Deserve Fudge Always”. I’m not aware of a common device for the spaces of the bass clef.
One thing to notice with the bass clef is that the notes names are one line or one space lower than in the treble clef. But thinking this way in the long run is not efficient.
Ledger lines are used to extend the staff higher or lower than it would otherwise allow. Ledger lines are like mini lines that extend above or below the staff. It is important to space ledger lines equal to the spacing of the lines of the staff.
Middle ‘C’ (C4): There is an area of overlap between the bass and treble clefs. The middle point between the two staves is called ‘Middle C’ and corresponds with the most central C note on the piano keyboard. Identical pitches (notes of the same pitch) are circled in the above example.
The diagram below shows the relationship of the grand staff to the piano keyboard.
To notate scales other than C major and its related modes, sharp (♯) and flat (♭) signs, called accidentals, are necessary to maintain the interval structure. A sharp raises a note by one semitone (the interval that occurs between any adjacent two keys of the keyboard), and a flat lowers a note by one semitone. The natural (♮) resets any previous accidental.
The most problematic issue with notating scales is in dealing with the semitones that occur between B and C, and E and F. In the modes of C major, there is no problem as the semitones are built into the tuning and notation system.