please explain this code if you can

I am working on learning how to build an admin area for my theme. I don’t understand how and why to use the following functions. I have read through the codex on these functions but still do not understand. Can you put it simply?

register_setting
add_settings_field()
add_settings_section()
settings_fields()

I have been googling the crap out of the wordpress admin area and have found 5 different ways to do this. This is the latest method. I do have a form set up and I am testing. This is what I have now

add_action('admin_menu', 'omr_create_menu');

function omr_create_menu() {

	//create new top-level menu
	add_menu_page('Paradiso Options', 'Paradiso options', 'administrator', __FILE__, 'paradiso_settings_page', 'favicon.ico');

	//call register settings function
	add_action( 'admin_init', 'register_mysettings' );
}

function register_mySettings(){
	register_setting('paradiso_group','paradiso_introText');
}

function paradiso_settings_page(){
	?><div class="wrap">
		<h2>Paradiso Options Page</h2>

		<form method="post" action="options.php">
			<?php settings_fields('paradiso_group'); ?>
			<table class="form-table">
			<tr valign="top">
				<th scope="row">Intro Text</th>
					<td><input type="text" name="paradiso_introText" value="<?php echo get_option('paradiso_introText');?>" /></td>
			</tr>
			</table>
			<p class="submit"><input type="submit" class="button-primary" value="<?php _e('Save Changes') ?>"  /></p>
		</form>
	</div><!--END wrap-->
	<?php
}
?>
<?php

I don’t understand why in the form I need this line
<?php settings_fields('paradiso_group'); ?>

For this one setting, is the code complete? am I missing anything? Is there a better way?

Thank you for taking the time to answer this post. Your time is appreciated