This Andante is the slow movement from Mozart's Piano Concerto No. 21 in C, although the movement itself as tradition demands is not in the home key of the work (C, a key signature with no sharps or flats) but in a related key, in this case F (with a key signature of 1 flat). This work will seem quite familiar to most people having been used frequently on television, and often appearing on albums of relaxing (or "chillout") classical music. The movement is most often associated with the title "Elvira Madigan" which comes from a relatively obscure Swedish film dating from 1967. Unlike the concertos of later composers, some of Mozart's Piano Concertos can be attempted by amateur pianists. This does not mean that they are easy to play, just not quite so difficult. If you prefer, here is an arrangement of this movement for piano solo where the piano plays the solo and orchestral parts. The video below illustrates the music in the form of a piano roll animation, or below that you can play the mp3 file and see the sheet music scores.
For the orchestral version, the following sheet music parts are available for free download and printing for personal use: the Conductor's Score, the Piano Part (soloist), and parts for all the orchestral instruments flute, oboes, bassoons, horns, 1st violins, 2nd violins, violas, and cellos and basses. More sheet music for Mozart's Piano Concertos can be found at these search links Sheet Music Plus (US) or The Music Room (UK).