Drop down Menu Submit

I need to know how to set up my first drop down menu so that when a user selects a n item from the drop down menu it updates the second drop down menu. Its not so much as needing to know how to update the second drop down menu, but needing to know how to make it so that the form is submitted when the user selects the first item as opposed to having to select an item then pushing a submit button.

Thanks

Also in #HTML _↴