Models in Caribou are a representation of the data of your application. Models can be created like any content, but models are special in that creating a model enables a new type of content to be created. Conceptually there should be a model for every variety of real world data that the application is capturing. Each model has a set of Fields which represent the different types of data that the model keeps track of. These fields can be of a variety of types, things like text, images, numbers, dates, and even associations to other models.
As an example, to create an application that lets you create presentations, you could have a Presentation model that would have a “title” text field and maybe a “preview” image field, and a Slide model with a “caption” text field and an "image" field with an image containing the slide content. Then, you could create an association between Presentation and Slide so that Presentation has a collection of Slide objects. Once these models are created, you could start creating Presentations and populate them with Slides.
This flexibility in defining what kind of data your application will contain enables an endless variety of possible applications to be built. Once a model exists in the system, you can read data from the API or create new content in the Admin.
Model itself is a model, with a collection of Fields (which is also a model!) To read more, check out the Introduction to Data Modeling.
Pages are the way to define how urls are matched in your application. Each page represents a route that can be matched when a user navigates to a particular url. Once a route is matched, the controller associated to that page is triggered with the parameters defined by that route. Pages form a nested structure, so if a page is a child of another page, it inherits its parent's route and adds its own unique path onto it. In this way the routing structure of an application can be organized hierarchically, simplifying what could otherwise be a complicated tangle of routes.
Read more at Defining Routes and Pages.
Once a route has been matched, the corresponding controller is triggered. A controller in Caribou is just a Clojure function that takes a single argument, request, and generates a response based on the information contained in the request.
A controller can be thought of as the code glue that links requests to responses. This can be as simple as directly rendering a static template in the most basic case to creating models, hitting remote apis, writing files, image manipulation, or really anything that can be programmatically accomplished (which is quite a lot these days!)
Everything you need to know about Controllers is here
In practice, a controller can use the built in template system called Antlers to render html or json (or any other format for that matter). Any parameters passed into the built in render call will be available in the template.
Templates are simple text files with portions which can be substituted out dynamically. This is the difference between static sites, which only ever display the same thing over and over again, and a fully dynamic website which can respond in endless ways depending on what is desired.
To see more on how this is done, check out the section on Rendering Templates