radio button

I’m in need of some help.
Ive a radio button on a plugin option page. The code segment is:
function ships_track_units_settings_input() {
$options = get_option( ‘ships_track_units’ );
$text_string = $options[‘text_string’];
echo “<input name=’ships_track_units_main’ type=’radio’ value=’English’ checked /> English (m/h,ft)
“;
echo “<input name=’ships_track_units_main’ type=’radio’ value=’Metric’ /> Metric (km/h,meters)
“;
}
echo “<input name=’ships_track_units_main’ type=’radio’ value=’English’ checked /> English (m/h,ft)
“;
echo “<input name=’ships_track_units_main’ type=’radio’ value=’Metric’ /> Metric (km/h,meters)
“;

As a newbe this code is just a guess but what I don’t know is how the database saves the data, and how my page changes the the butoon to reflect the users choice.
Thanks in advance.
Ron