There are various types of notes, each of
which is held for a different length of time.
The way a note appears indicates how many beats
it should last.
In most music:
Whole notes last four
beats.
Half notes last two
beats.
Quarter notes last one
beat.
Any note shorter than a quarter note has
one or more "hooks" to indicate its
length. Each hook cuts the note's length
in half.
Eighth notes (one hook)
last one-half beat.
Sixteenth notes (two
hooks) last one-quarter beat.
These continue on to thirty-second and
sixty-fourth notes (with three and four
hooks, respectively). If two or more
notes requiring hooks appear in a row,
they're often connected with "beams."
The number of horizontal lines in a beam
indicates note length.
Two eighth notes
connected by a beam
Music also has rests, which indicate
silent beats. They're counted in the
same way as notes, and correspond to the
notes they represent.