a short explanation
From experience and from what I have seen and read, forms can serve many purposes cause there are lots of different kinds. They contain the principles of movement of a given art. They give order and connection between movements. This aids in learning how to shift from one stance to another, moving the body as a whole, learning how to breathe while moving, and last, but not least, circulating energy in the correct fashion.
This is not the same as fighting. Now, there are fighting sets, which are stereotyped fighting situations, but that is not what we are discussing here. Here, I am talking about solo forms.
Fighting is something else. Theoretically and in practice, in my opinion, you do not need forms in order to be a fighter. I believe you can learn the stances, the fists, the transitions and the applications, energy, without them, practicing units of movement repetitively and changing their order. Yet, the training can be enhanced by them, by the organization they offer to it. They serve to define and organize an art.
I guess one of the most elementary and important are the stance training forms, in which one goes from one stance to another using only leg work. Forms go on to include the fists, and weapons, extensions of the body.
The applications are within the forms, but doing forms is not equivalent to working out applications as in a contact situation with another human being. And, in fact, practice in these contact situations simultaneous with or before learning forms is most efficient, as one has a feeling for the moves and knows the components of them and what they mean in physical contact before learning the form. However, unfortunately, this is not always done.
In fighting, there are no rules. Not in real fighting. The person does not necessarily move as you would expect, or wait for you to complete a move. In a form, there might be many components to a unit (a small set of moves), but in a real fight you do not necessarily need all of the components or follow the order of the forms in delivering them.
You fight in terms of the stances, fists, kicks and energy training. The forms are a blueprint of an art, with information that is not obvious. A fight is freestyle, using the principles you have learned in order to prevail, to respond properly. A form is a form, a tool on many levels.
Cody