Creating a Custom Metabox in Wordpress

I'm trying to create a custom metabox in Wordpress for a custom post type. I found a nice little tutorial that actually explains it rather well:

http://wptheming.com/2010/08/custom-metabox-for-post-type/

The only part of the tutorial that I don't understand is where he adds the text input field.

// The Event Location Metabox
 
function wpt_events_location() {
    global $post;
 
    // Noncename needed to verify where the data originated
    echo '<input type="hidden" name="eventmeta_noncename" id="eventmeta_noncename" value="' .
    wp_create_nonce( plugin_basename(__FILE__) ) . '" />';
 
    // Get the location data if its already been entered
    $location = get_post_meta($post->ID, '_location', true);
 
    // Echo out the field
    echo '<input type="text" name="_location" value="' . $location  . '" class="widefat" />';
 
}

I don't know where "wp_create_nonce( plugin_basename(__FILE__) )" comes from or what exactly it does. Having said that, I'm actually looking to have checkboxes in my metabox rather then an input field. But because I don't completely understand the code behind adding an input field, I'm not entirely sure what I would need to do for checkboxes. Can someone help me out?

A second part to that question—is it possible to configure it so that it is mandatory for an author to select one of the checkboxes in my custom metabox before they can publish the post?