Sharp symbol is used in sharped notes.
Sharped notes are written by putting a sharp sign (#) before it.
All sharped notes  go up a half tone or semitone higher than its basic note equivalent and
this effect is carried out for the rest of the bar it is written on (This means that all notes that proceeds after a sharped note witin the same bar, on the same line or space as the sharped note will also go up by a semitone even if there is no sharp symbol (#) written beside them.). This converts the note from a basic note to an intermediary note (as a sharped note). (See example below)

It is also used as a key signature. If used as a key signature, all notes with the same name (for example note "C") where the sharp key signature is written on (whether it is on a space or a line) go up a half tone or semitone higher even if there are no sharp symbols written before these notes and this is carried out for the whole staff, the sharp key symbol is written on. This convert all affected notes from basic notes to intermediary notes (as sharped notes) (See example below)
 
 

Flat symbol is used in flated notes.
Flated notes are witten by putting a flat symbol  before it.
Flated notes  go down a half tone or semitone lower than its basic note equivalent and this effect is
carried out for the whole bar it is written on (This means that all notes that proceeds a flated note  within the same bar, on the same line or space as the flated note will also go down by a semitone even if  there is no sharp symbol written beside them).This converts the note from a basic note to an intermediary note (as a flated note). (see example below)
It is also used as a key signature. If used as a key signature, all notes with the same name, where the flat key signature is written on (whether it is on a space or a line) go down a half tone or semitone lower even if there are no flat symbols written before these notes and this effect is carried out for the whole staff the flat key signature is written on. This convert all affected notes from basic notes to intermediary notes (as a flated note). (see example below)
The Flat is written with the symbol .

The effect of sharp and flat symbols are negated by Naturals which brings back the note to its original tone as a basic note for the rest of the bar it is written on. 

Naturals are written with the symbol .

Key Signature

Key Signatures are symbols written just at the right of the clef symbol which specify which notes automatically
go up a semitone higher (sharp) or go down a semitone lower (flat) than it is actually written.

If a staff is written without a key signature, it is in the key of C.

Two types of key symbols used in music are sharps and flats.

With sharp key sinatures; all notes with the same name on the space or line where the sharp symbols are written  automatically go up a semitone higher for the whole staff even if there are no sharp symbols written beside them.

Here is an example of sharped notes and sharp key (Key of A):

(Don't worry. You do not even have to know the name of the key.)

From the above figure we can see that three sharp key symbols are used to denote the key of  A.
These sharp key symbols on the staff are on the 3rd space from the bottom, 5th line from the bottom, and the first Ledger space on top of the staff (which corresponds to the basic notes C, F and G we saw in PART I of this tutorial) and as a result of this;

all notes C, F and G on this staff automatically go up higher by a semitone to C#, F# and G#, unless negated by a natural symbol.

The effect of the sharp key symbols are negated by naturals only for the rest of the bar where it is written as shown
on the 2nd, 3rd, 6th and 8th notes on the above staff.

The 4th note A# is an example of a sharped note. (If there was an A note on this first bar after A#;  it would also go up a semitone higher even if the # sign is not written before it.)
 

Here is an example of flated notes and flat key (Key of E-flat):
 

Take note of the 3rd note on the first bar. It assumed basic note A even without the natural sign.
Take note of the 4th note on the 2nd bar. It assumed intermediary note G-flat even without the flat sign.
Take note of the 3rd note on the 3rd bar. It assumed inter
 
Now let us go to Part IV

If you have any comment on above subject please write me.

Thanks to Monica for her great advice.

Rudy Ong
(Webitor)