:unsure: Where is the clear documentation of every detail of k2..

The target is to know about the feature that allows the users to build forms..

As per the feature list.. there is something like "user forms"

guide me please..

Hi. There is no form builder in K2. You can find resources about K2 at getk2.org/documentation . Regarding forms, you can add extra fields to specific categories. K2 is a free extension so you are highly encouraged to try it and see if it fits your needs.

as per the home page of k2...

its has got "rich content forms for items" and " a powerful plugin API to extend item/category/user forms"..

Where do i come to know more about it..

its no where

The plugin api refers to the k2 events that are built in to fire k2 plugins. Look thru the extend k2 for the example plugin and read the code in it.

The rich content is shown when you add a new k2 item and have allvideo and sig installed, as the item by default will contain image, text, video, attachment, and gallery