Forms are present in every martial art. They are a series of predetermined techniques that are arranged in a certain order, which are meant to be practiced from start to finish.
They are not meant to teach a student how to fight because, after all, no opponent or assailant will move in a predictable pattern. Instead, they are meant to teach proper body mechanics and structure of the techniques.
The legendary Bruce Lee did away with forms, as he thought they were an example of "organized despair." However, it must be kept in mind why he felt this way: Bruce was looking to develop fighting skills as quickly as he could. If one thinks of forms that way, then yes, you could make the argument they are useless.
There is no doubt that Bruce Lee was ahead of his time, but in my opinion his view of forms was short-sighted. I believe they are an important part of training, as they give students something they can do on their own as "homework."
Wing Chun has 6 forms total. If you click on the name of each form, you will be taken to a page that goes into further detail and also provides a video of each one.
A NOTE ABOUT THE WOODEN DUMMY, POLE, AND KNIVES
On this page, I provide the Chinese name of the Wooden Dummy, Pole, and Knives, followed by the English translation. However, going forward I will be using only the English names for those forms.
After all, I've met people who've studied Wing Chun for 20+ years who say "Pole" instead of "Luk Dim Boon Kwun." :-)
TRANSLATION: "Little Idea"
This is the first form a Wing Chun student learns. However, it is not a "beginner form," meant to be forgotten once the student moves on to the next level. Even people who have been doing Wing Chun for 50 years or more still practice their Sil Lum Tao. It teaches the basic training stance and the most common hand movements. There is no stepping, kicking, or rotation of the torso in this form.
TRANSLATION: "Seeking the Bridge"
In this form, the student learns to:
TRANSLATIONS: "Darting Fingers" or "Thrusting Fingers"
Also known by some as the "desperation form," this form contains moves that you would use if you lost control of the centerline. It includes many techniques that are quite painful, like elbow strikes and finger jabs.
TRANSLATION: "Wooden Dummy"
This is one of the tools most associated with Wing Chun. Basically, you are taking all the tools you learned in Sil Lum Tao and Chum Kiu and applying them to something that takes up physical space, instead of just practicing the techniques in the air.
TRANSLATION: "Six and a Half Point Pole"
The translation is not indicative of the length of this weapon, which is actually around nine feet long. Instead, it is related to the number of sections in the form, with the final movement of putting the pole down being considered "half" of a move.
This weapon would obviously be used at a much longer range than the rest of Wing Chun's arsenal. Some lineages choose to teach this form last, since it goes against the grain of everything else the students learn.
TRANSALTION: "Eight Slashing Knives"
I'm honestly not sure why it is called "Eight Slashing Knives" when a student can hold only two at a time, although my guess is it's similar to the way they named the Pole form: there are eight sections. The Knives are an extension of the hands, and many of the moves in this form will look familiar.