How was the first clarinet created?

There was no first clarinet. The clarinet was derived from the chalumeau, a single-reed instrument which had a cylindrical tube and a bell. The chalumeau had a range of about an octave and a half, and was used in folk music and military bands. In the 18th century, the chalumeau was modified by adding a second key, which extended its range by a semitone. This instrument became known as the "clarinette", and was eventually standardized into the clarinet we know today.