Wordpress custom field (select) to posts

I'm trying to understand plugins by making one. It puts a new menu to Wordpress Admin menu "Propagandas (ads)", which creates a post type "propaganda_item".

Since I need the user to choose a State/City for each "Propaganda", I've made an SQL table with City/State.

So far, so good, but now I don't know how to put the php select combobox in the "Propaganda" edit page. Example of what I mean

Actually I know how to populate the Select, but not how to put it within the post through my plugin.

Oh, and here is my plugin code:

<?php 
/*
Plugin Name: Frankec
Plugin URI: 
Description: propagandas
Version:1
Author URI:
*/?>

<?php// Registra Propagandas

function register_cpt_Propagandas() {

$labels = array(
    'name' => _x( 'Propagandas', 'propaganda_item' ),
    'singular_name' => _x( 'Propagandas', 'propaganda_item' ),
    'add_new' => _x( 'Nova', 'propaganda_item' ),
    'add_new_item' => _x( 'Adicionar Propagandas', 'propaganda_item' ),
    'edit_item' => _x( 'Editar Propagandas', 'propaganda_item' ),
    'new_item' => _x( 'Nova Propagandas', 'propaganda_item' ),
    'view_item' => _x( 'Ver Propagandas', 'propaganda_item' ),
    'search_items' => _x( 'Procurar Propagandas', 'propaganda_item' ),
    'not_found' => _x( 'Nenhuma Propaganda encontrada', 'propaganda_item' ),
    'not_found_in_trash' => _x( 'Nenhuma Propaganda encontrada no lixo', 'propaganda_item' ),
    'parent_item_colon' => _x( 'Propagandas-pai:', 'propaganda_item' ),
    'menu_name' => _x( 'Propagandas', 'propaganda_item' ),
);

$args = array(
    'labels' => $labels,
    'hierarchical' => true,
    'description' => 'Propagandas por Cateoria',
    'supports' => array( 'title', 'editor', 'thumbnail'),
    'taxonomies' => array( 'genres' ),
    'public' => true,
    'show_ui' => true,
    'show_in_menu' => true,
    'menu_position' => 5,
    'menu_icon' => 'dashicons-images-alt2',
    'show_in_nav_menus' => true,
    'publicly_queryable' => true,
    'exclude_from_search' => false,
    'has_archive' => true,
    'query_var' => true,
    'can_export' => true,
    'rewrite' => true,
    'capability_type' => 'post'
);

register_post_type( 'propaganda_item', $args );
}

add_action( 'init', 'register_cpt_Propagandas' );


function remove_menus(){


 remove_menu_page( 'edit-comments.php' );          //Comments    

}
add_action( 'admin_menu', 'remove_menus' );



?>

Thanks in advance guys! =)

via Chebli Mohamed