Here are some small forms that are commonly used in classical music:
This form consists of two sections, each ending with cadences, where the first section modulates to a different key and the second section returns to the original key.
This form is often explained as a statement, digression, and restatement. It’s comprised of three sections with the middle section being noticeably different than the first and last.
Rounded Binary: A|BA
This form is a variation of the Binary with an important distinction, the A material returns in a shortened state at the end to conclude the piece. One important difference between Rounded Binary and Ternary is that the B material in Rounded Binary is typically too short to stand on its own and is usually built from the A material.
The Strophic form is typically used in songs. This form is typified by a repeating section that is accompanied with a different set of lyrics.