Classical music is very prolific with lots of forms. There are Strophic, Binary, Ternary, Rondo, Sonata, Sonata-Rondo and many other forms.
Main feature of all of them is the content of elements or structure and by analysing them we come to the point where we are able to understand the piece. Every form has the main theme which is a recognizable melody upon which part or all of a composition is based.
In classical music there are lost of theme types. On WKMT website you can find the article written by me, analysing one in particular called The Period- eight measures long one type of theme and contains two four-measure phrases called Antecedent and Consequent.
For more information please click the link below, and also follow my personal Haydn project: Sonatas Analysis.