The form being used here is an active form. As you go through the elements, fill in the information where requested and at the end, you will be able to submit this form and see the results both via e-mail and with an automatically generated HTML page. Where appropriate, the resulting element will be displayed and you are encouraged to enter information or make choices. In this case, your form will send this element along with the rest to be processed by the CGI script and the resulting e-mail message will be sent to the address specified. The value of this element will be whatever the user types in.
Browsers are, in some cases, going to display HTML documents differently.
As you can see, you are allowed to select only one of the three choices presented. Also note that each element has the same NAME value. Unlike the radio type, users may choose any or all of the items. Often it is practical to offer users a list of choices of which you want them only to select one. In this case it was unnecessary as the option items will be passed along to the CGI script.