Model is the classes providing data, service related to data and business logic. This class works directly with data and provides data for other elements. In a module, these classes are contained in Model folder.
View is the classes which define data presented method (not update data). These classes are contained in the folder Block of module.
Controller is the classes which control application stream. They receive input which is requirement of users through HTTP request, transfer those requests to the classes which process the requests directly. From the link, Router will get to Controller which controls that link. In Magento module, these classes are contained in controller folder.