A form's purpose is to collect data and do something with the data that was submitted. All forms need to implement the \Drupal\Core\Form\FormInterface interface. The interface defines a submit method. Once the Form API has invoked the class's validation method, the submit method can be run.
This recipe will be based on the custom module and form created in the Creating a form recipe of this chapter. We will convert the form to \Drupal\Core\FormConfigBaseForm, allowing us to save our configuration and reuse code provided by Drupal core.
