Well, the user selects the checkbox in the browser. Then they either press a button to submit the form, or sometimes Javascript is used in what is commonly called AJAX to ,based on a browser event (e.g. clicking a checkbox), fire off a request to the server, and then the page is dynamically updated using javascript again. Here's an example...
You click a checkbox, and then the browser sends information, about which checkbox was checked, to the server, and the server then deletes a record in the database, and sends a success message back to the browser. The browser receives the message and displays a green bar on the top of the screen saying, this was deleted.
Good examples of that can be found in Gmail.
Let me know whether it is AJAX that you have in mind or just submitting a form.
I hope that helps!
Dan Bernardic
http://dan.bernardic.ca