Classification of classical music? How to distinguish symphony, sonata, concerto and serenade?

Many, many musical instruments together, that's called symphony. If one or several of them are dominant and compete with the whole band, it is the ×× concerto. Only a few instruments are chamber music, usually called ×× several ensembles. Sonata is usually a solo of an instrument, sometimes accompanied by an instrument. As for serenade, it is not a classification system with them. Solos and orchestral ensembles may be serenades.