Note pitches can be modified by using accidentals:
Accidental Name Effect sharp Raises the note 1 half step flat Lowers the note 1 half step double sharp Raises the note 2 half steps or 1 whole step double flat Lowers the note 2 half steps or 1 whole step natural Cancels any previous accidental
In music writing an accidental affects every note of the same name and in the same octave within a measure. In the following example the last G note is sharp (we would need to add a natural sign if we wanted it natural):
Go to Whole and Half Steps for more information on accidentals and their relationship to the piano.