The program services the request, assembles the results into an HTML document, and transfers control back to the Server, which transmits the document to the Browser. CGI programs are the good news and the bad news of Web interactivity. The good news is that the CGI program can do whatever is desired. Here is an inactive example of a form. There are active forms elsewhere in Web 101.
Check boxes are for closed-ended answers, where any number of options can be chosen.
You will see that you can click any number of these. You can select all of the boxes, none of the boxes, or any number in between. However, radio buttons work like those very old radios. You selected a station by pushing a button. As soon as you selected one button, you deselected all of the others.