Conceptually it isn't difficult. The controller (e.g.
servlet) gathers the request parameters and performs whatever actions are required to update the application's state. This could include updating a database or storing data in the user's session or sending e-mails or whatever other business requirements need to be performed. Then it collects together all of the information required to produce the HTML which is to be sent to the client as the response, and forwards to the view component.
The view (e.g. JSP) takes the information which the controller produced, and generates HTML based on that information.
Note that it isn't the view's responsibility to update the application's state in any way. That's why removing an attribute is a dubious idea for a JSP.