Joomla! Documentation™

The underscore function of JRoute is used so that the site displays SEF URLs; see Supporting SEF URLs in your component.
The "task" field is used to define the controller.task parameter which will be sent to the server in the POST request when the form is submitted.
The "boxchecked" field is used to keep track of the number of checkboxes ticked.
Using the form token helps prevent CSRF attacks.