The Harpsichord was a stringed keyboard instrument in which the strings were plucked to make sound. It was developed in the 14th Century and was superseded by the Piano in the early 19th Century.
The Harpsichord used a plucking mechanism in which to create its sound. For each string of each note, a small piece of material called a "plectrum" is attached to a slip of wood called a "jack", and rests on the under side of the string on the far end of the key, so when the key is hit the far end rises, plucking the string as it does so. The jack is pivoted so that when the key is let go the plectrum slides and does not touch the string a second time. Unfortunately, there were a few bad aspects about the Harpsichord. One being that the dynamics of the notes on the keyboard would stay the same no matter how hard or softly they would be played. This problem was counteracted by various techniques and methods invented to change the notes volume. After this problem aroused, Harpsichords were soon made with two strings per note instead of one and a row of jacks for each set of strings. "Stops" and "Registers" were invented, to allow the player to move unwanted jacks just out of reach of each string, and therefor allowing the player to alter the volume and combination of tone colours. One set of strings sounded an octave above normal pitch, where as some German Harpsichords had a set of strings that sounded an octave lower than normal pitch. Some Harpsichords were then made with two keyboards, or "manuals", to allow further alteration with volumes and tone colours. .
On the piano, essentially, when a key is pressed down, its tail pivots upwards and lifts a lever that throws a hammer against the string of that note. At the same time, a damper is raised from the string to allow it to vibrate more freely. This is how a piano creates its sound. When the key in question is fully released everything falls back into place because of gravity.
