Settings API Demo

plugin.php

<?php
/**
 * Plugin Name: My Plugin
 * Plugin Description: Settings API Demo
 */

add_action( 'admin_menu', 'my_admin_menu' );
function my_admin_menu() {
	add_options_page( 'My Plugin', 'My Plugin', 'manage_options', 'my-plugin', 'my_options_page' );
}

function my_options_page() {
	?>
	<div class="wrap">
		<?php screen_icon(); ?>
		<h2>My Plugin Options</h2>
		<form action="options.php" method="POST">
			<?php settings_fields( 'my-settings-group' ); ?>
			<?php do_settings_sections( 'my-plugin' ); ?>
			<?php submit_button(); ?>
		</form>
	</div>
	<?php
}

add_action( 'admin_init', 'my_admin_init' );
function my_admin_init() {
	register_setting( 'my-settings-group', 'my-setting' );

	// Sections
	add_settings_section( 'section-one', 'Section One', 'section_one_callback', 'my-plugin' );

	// Fields
	add_settings_field( 'field-one', 'Field One', 'field_one_callback', 'my-plugin', 'section-one' );
}

function section_one_callback() {
	echo "Some help text goes here.";
}

function field_one_callback() {
	$setting_value = esc_attr( get_option( 'my-setting' ) );
	echo "<input class='regular-text' type='text' name='my-setting' value='$setting_value' />";
}

Most helpful for setup of settings page in WordPress admin.