<form method="get" action="foo.php">
   <select name="item" mutiple>
   <option>1</option>
   <option>2</option>
   <option>3</option>
   </select>
   <button>go</button>
   </form>

If you select option 1 and option 3 it will submit to foo.php?item[]=1&item[]=3

So in general <form method="get"> will append a query string to the action url composed of the form field values. But it is not possible to specify an url template to control the exact structure of the url. If you want that you have to implement a server side redirect.

One thing I did not know until recently myself: form submit buttons can specify their own formaction and formmethod attributes that override that ones specified by the form. So you can have multiple buttons inside on form the submit to different locations.