What is Musical Form?

— musical form, the structure of a musical composition. The term is regularly used in two senses: to denote a standard type, or genre, and to denote the procedures in a specific work.

What are the different musical forms? Differentiate one from the others?

— Four basic types of musical forms are distinguished in ethnomusicology: iterative, the same phrase repeated over and over; reverting, with the restatement of a phrase after a contrasting one; strophic, a larger melodic entity repeated over and over to different strophes (stanzas) of a poetic text; and progressive, in which new melodic material is continuously presented (thus synonymous with through-composed). 

What are the functions of repeated marks in relation to musical forms?

— Repetition is important in music, where sounds or sequences are often repeated. It may be called restatement, such as the restatement of a theme. While it plays a role in all music, with noise and musical tones lying along a spectrum from irregular to periodic sounds,(Moravcsik, 114)(Rajagopal) it is especially prominent in specific styles

A literal repetition of a musical passage is often indicated by the use of a repeat sign, or the instructions da capo or dal segno.

Repetition is a part and parcel of symmetry—and of establishing motifs and hooks. You find a melodic or rhythmic figure that you like, and you repeat it throughout the course of the melody or song.