The harp is an old instrument. It is used in the modern orchestra but not very often. The notes are sounded by the performer plucking the strings with the fingers. The harp has pedals so the notes can be changed to flats, naturals or sharps.
The range of the harp is from two to six octaves but this depends on the size of the instrument. The music is written on the treble and bass clefs.
The harp is famous for its glissando technique. This is where the fingers sweep rapidly across the strings and create a scale either ascending (up) or descending (down).
Below is a picture of a harp.
The strings of the harp up close.
The strings of the harp being plucked by the performer.
Warburton, Annie O. Basic Music Knowledge. Cambridge: Cambridge University Press, 1995. Print, p. 148.