Seeing your other questions, I suspect you are talking about web application frameworks.
There are different web application frameworks which use different concepts. Some of them are action based, such as Struts and Spring Web MVC and some of them are component based, such as JSF and Wicket.
In an action based web app framework, you write classes that represent actions by the user, for example "view customer details", "submit an order", etc. Those action classes should get the data submitted with the HTTP request and work with it.
In a component based web app framework, the things that a user interacts with on a web page (such as text boxes, buttons, links etc.) are represented by components which hide the low-level details of the HTTP request, response etc.
It's hard to explain it in just a few sentences. You can lookup the documentation of the web app frameworks I mentioned above.