My first reaction was "If you want checkboxes, why does the code call for 'select', which means dropdowns?" My second reaction was: How can you use checkboxes if each category has two or more mutually exclusive options? For that you'd need radio buttons if you want something visible. (Yes, technically you could use checkboxes, but then you'd also need a bunch of extra code to ensure that the user has selected exactly one item in each category.)
That takes us to answer #3: You gotta give us a hint. How much about forms do you already know? Is this an existing form of your own that you want to tweak, or something you found online and you have no idea what part does what?
Well, the horse's mouth is here [w3.org...] but frankly their html pages scare me to death. (The css pages are fine.)
Quick cut-and-paste from the nearest form I've got handy:
<input type = "radio" name = "keepdate" value = "fulldate">Full Date<br> <input type = "radio" name = "keepdate" value = "divider" checked = "checked">Divider<br> <input type = "radio" name = "keepdate" value = "none">Nothing
<input type = "checkbox" name = "keepline" value = "opt_ip">IP<br> <input type = "checkbox" name = "keepline" value = "opt_mth">Method<br> <input type = "checkbox" name = "keepline" value = "opt_page">Page<br>
Note the name of each item. Forms are one of the few places the name attribute is still used. To keep radio buttons together, they all have to have the same name.