Models: These are the classes that represent the domain you are interested in. These domain objects often encapsulate data stored in a database as well as code that manipulates the data and enforces domain-specific business logic. With ASP.NET MVC, this is most likely a Data Access Layer of some kind, using a tool like Entity Framework or NHibernate combined with custom code containing domain-specific logic. Data validations is also implemented in model classes.
View: This is a template to dynamically generate HTML.
Controller: This is a special class that manages the relationship between the View and the Model. It responds to user input, talks to the Model, and decides which view to render (if any). In ASP.NET MVC, this class is conventionally denoted by the suffix Controller. All Code logic is implemented in this section.