Options for plugin select menu

[mtjo]

I cannot find any docs on how to write the code to populate the options for a plugin select box.

Code:

$setting = array(
        'sid'         => 'NULL',
        'name'        => 'setting name',
        'title'       => 'setting title',
        'description' => 'setting description',
        'optionscode' => 'select',
        'value'       => '?',
        'disporder'   => '13',
        'gid'         => intval( $gid )
    );
    $db->insert_query( 'settings', $setting );

How do I write the default value?