At first for me this concept was a bit hard to grasp, hopefully i can break it down to basics here.

The Model-View-Controller is basically a design theory and a very logical organization of the parts or an iPhone application.

Model is basically the classes that hold your application’s data. For example if you created an application that when a button was pressed would take the name of that button (a string) then output that string to a label or a text field, then in this instance the Model object would be the string itself, the actual data that was used and transferred. This is a very loose example actually but, its simplicity I think makes the Model object more understandable. Most application that use a Model object will be storing or preserving data like when using Core Data classes. Read More

Actions are methods that are part of your controller class and are declared with a special keyword, IBAction.  This keyword tells Interface Builder that this is an action and can be triggered by a control.  In short if you want to have interface objects in the nib (like buttons) trigger methods in the controller class then you would use special methods called Actions. Read More