The Andante in C is a keyboard work, K. 1a, written by Wolfgang Amadeus Mozart in 1761 and found in Nannerl's Music Book. It is not just Mozart's first keyboard work, but his first (or so believed) composition. It is an extremely short piece (just 20 seconds long), likely notated by his father, Leopold Mozart, due to Wolfgang's being just 6 years old at the time.
It is normally performed on the harpsichord and is in the key of C. The piece opens with a lively one barphrase, which is repeated piano (quietly). This is done again with a second, modified phrase - before it gains a deeper, unrepeated phrase and ends.
Mozart, his life story, and several classical music pieces by him are here; Mozart was one of the greatest composers ever - Mozart was a master composer of classical music.
Mozart's music from the next decade - and it came at a blisteringly prolific rate - was only sporadically popular, and he eventually fell back on his teaching jobs and on the charity of friends to make ends meet.
Mozart was a master of counterpoint, fugue, and the other traditional compositional devices of his day; more than this, Mozart was perhaps the greatest melody writer the world has ever known.