Sonata form, for instance, is made up of three or four sections: Exposition, Development, Recapitulation, and optional Coda. Within the exposition are two (occasionally three) contrasting main melodic themes. The exposition is played twice before the development begins, a direct, literal repetition of those first themes. The development takes the themes and plays with them, varying their keys and mood, sometimes dovetailing or entirely overlapping them. Then the recapitulation is almost a direct repetition of the exposition, with the usual change that the second theme is now in the same key as the first theme. If there’s a coda, it’s a sort of second development that leads to a satisfying conclusion. The pattern of repetition of the themes and sections is what makes sonata form sonata form.