MVC is a design pattern. That means it is a basic concept for the design and architecture when developing a software. Using a design pattern can be good for various reasons. It makes you put a structure in the project , wich helps you when you need to debug the code , add modules or upgrade your software to a new environment.
In the case of MVC the idea is to split the part of the software wich represents and handles the data (model) from the part of the part of the software that views the data (view). Any kind of data is represented by a model. To view or edit the data in a view a controller is needed.

Jnex is a framework that is based on the MVC pattern. That means it provides components (default implementations or abstract classes and interfaces) for models, views and controllers that are easily expandable and open source. Thats not all but to give you an overview of jnex's most important components see the scheme below. Jnex models inherit all from one abstract class but are divided into models that represent simple value data and models that represent composite data (arrays and stuctures).

This the Architectural Overview Document for jnex.

Here is a brief overview on making webapps with jnex. It is recomended to look at the commented HTML-Example on this site to see how the basic concept is realized. This graphic is a simplified view, a lot more components are involved. It shows the components you have to care about if you want to write a web app with jnex.