The FORM of music is the internal structure of a composition or a movement of the composition. The most basic form in music is called Variation Form.
VARIATION FORM - In Variation Form, one main theme is presented and then repeated any number of times, each repetition including minimal to large scale musical changes. A schematic of Variation Form would be: A A1 A2 A3 A4...
EXAMPLE - Symphony 94 "Surprise" - Haydn (2nd movement)