In standard notation, a single musical sound is written as a note. The two most important things a written piece of music needs to tell you about a note are its pitch - how high or low it is - and its duration - how long it lasts.
To find out the pitch of a written note, you look at the clef and the key signature, then see what line or space the note is on. The higher a note sits on the staff, the higher it sounds. To find out the duration of the written note, you look at the tempo and the time signature and then see what the note looks like.
The pitch of the note depends only on what line or space the head of the note is on. (Please see Pitch, Clef and Key Signature for more information.) If the note does not have a head (see Figure 1.34), that means that it does not have one definite pitch.
The head of the note may be filled in (black), or not. The note may also have (or not) a stem, one or more flags, beams connecting it to other notes, or one or more dots following the head of the note. All of these things affect how much time the note is given in the music.