The type of form table lists some common types of musical form.
Strophic form is A. It contains a single section. The section is repeated as many times as necessary.
Strophic is the simplest of all musical forms to write. Thousands and thousands and thousands of excellent pop songs, blues songs, folk songs and carols have been written in this form. There is an awful lot of mileage left in strophic. The downside is, of course, boredom. Constant repetition eventually whittles away the desire to live. Except for guitarists, who can happily blaze away all day playing the same old blues, the bass player and drummer having long since lapsed into a coma along with most of the audience.
Binary form is AB. It contains two sections A and B. Simple binary is AABB and rounded binary is AABA1BA1. In classical music A and B are usually the same duration. In pop music A and B constitute the verse and chorus and are usually of different length. There are all sorts of permutations: AABA is a simple and effective structure.
There are classification issues even in binary form. For example, if the B section is not radically different to the A section should it be classified as AB or AA1? You can easily get bogged down in these structural niceties of form. Classical music, in particular, seems to delight in an alphabet soup from Aria all the way up to, well, not Z, but Waltz at least. Actually, there is no classical form beginning with the letter Z, so I would like to volunteer Zydeco to fill the gap.
Ternary form or song form, is ABA. It contains 2 sections in 3 parts, with the first section A beginning and ending the piece. The logical ones among you will now be in despair about form. Ternary form is not the expected ABC but ABA. That is just the way it is, form is a flexible word. On the plus side, ternary is probably the most popular form in music. It is an excellent default structure for writing music.
Rondo form is ABACA. It has a repeating section, A, interleaved by new material, B, C etc. The repeat section A is usually short, the other sections are longer.
Arch form is ABCBA. It contains 3 or more sections. It is symmetrical and is the same backwards as forwards so it is also called palindromic form.
Medley is ABCDE. Every section is different. It is also known as through-composed form, music composed as a series of individual sections which differ from each other. Medley is the ideal form to use for all those old riffs you have stored away under the bed. Get them out, dust them off, string them together and call it a medley.
Theme and variation is AA1A2. It consists of a theme, A, followed by any number of variations A1, A2 and so on. The A theme is often based on a melody, and the variations are variants of that melody. In theme and variation, of course, variant A255 will have grown into a completely different beast and there may be no vestige of the original theme A left. This is why theme and variation is the ultimate in organic music. It is an excellent approach to composition if you enjoy exploring. All you need to start is a short melody, A, tweak it a little to become A1, tweak A1 to become A2, tweak A2 to create A3 and so on, ad infinitum. Fugue is an excellent example of this type of form.
This is not an exhaustive list of forms. For example, vocal music is sometimes separated from instrumental music, and pop music distinguished from the art song used in classical music.