<?php

/** Set Defaults **/
add_option( 'myplugin_field_1', 'some default value' );
add_option( 'myplugin_field_2', '1' );
add_option( 'myplugin_field_3', 'another default value' );

/** Add Settings Page **/
function myplugin_settings_menu() {

	add_options_page(
	/*1*/	'My Plugin Settings',
	/*2*/	'My Plugin',
	/*3*/	'manage_options',
	/*4*/	'myplugin_settings',
	/*5*/	'myplugin_settings_page'
	);

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

<?php

/** Settings Page Content **/
function myplugin_settings_page() {

	?>

	<div class="wrap">
		<?php 
		
		// Uncomment if this screen isn't added with add_options_page() 
		// settings_errors(); 
		
		?>

		<h2>My Plugin</h2>
		<p>Some text describing what the plugin settings do.</p>

		<form method="post" action="options.php">
			<?php

			// Output the settings sections.
			do_settings_sections( 'myplugin_settings' );

			// Output the hidden fields, nonce, etc.
			settings_fields( 'myplugin_settings_group' );

			// Submit button.
			submit_button();

			?>
		</form>
	</div>

	<?php
}

/** Settings Initialization **/
function myplugin_settings_init() {

     /** Setting section 1. **/
	add_settings_section(
	/*1*/	'myplugin_settings_section_1',
	/*2*/	'Section 1',
	/*3*/	'myplugin_settings_section_1_callback',
	/*4*/	'myplugin_settings'
	);
	
	// Field 1.
	add_settings_field(
	/*1*/	'myplugin_field_1',
	/*2*/	'Field 1',
	/*3*/	'myplugin_field_1_input',
	/*4*/	'myplugin_settings',
	/*5*/	'myplugin_settings_section_1'
	);

	// Register this field with our settings group.
	register_setting( 'myplugin_settings_group', 'myplugin_field_1' );
	
   /** Section 2 **/
	add_settings_section(
	/*1*/	'myplugin_settings_section_2',
	/*2*/	'Section 2',
	/*3*/	'myplugin_settings_section_2_callback',
	/*4*/	'myplugin_settings'
	);
	
	// Field 2.
	add_settings_field(
	/*1*/	'myplugin_field_2',
	/*2*/	'Field 2',
	/*3*/	'myplugin_field_2_input',
	/*4*/	'myplugin_settings',
	/*5*/	'myplugin_settings_section_2'
	);

	// Register this field with our settings group.
	register_setting( 'myplugin_settings_group', 'myplugin_field_2' );	
	
	// Field 3.
	add_settings_field(
	/*1*/	'myplugin_field_3',
	/*2*/	'Field 3',
	/*3*/	'myplugin_field_3_input',
	/*4*/	'myplugin_settings',
	/*5*/	'myplugin_settings_section_2'
	);

	// Register this field with our settings group.
	register_setting( 'myplugin_settings_group', 'myplugin_field_3' );
}
add_action( 'admin_init', 'myplugin_settings_init' );

function myplugin_settings_section_1_callback() {

	echo( 'Some info about this section.' );
}

function myplugin_settings_section_2_callback() {

	echo( 'An explanation of this section.' );
}

/** Field 1 Input **/
function myplugin_field_1_input() {

	echo( '<input type="text" name="myplugin_field_1" id="myplugin_field_1" value="'. get_option( 'myplugini_field_1' ) .'" />' );
}

/** Field 2 Input **/
function myplugin_field_2_input() {

	// This example input will be a dropdown.
	// Available options.
	$options = array(
		'1' => 'Option 1',
		'2' => 'Option 2',
		'3' => 'Option 3',
	);
	
	// Current setting.
	$current = get_option( 'myplugin_field_2' );
	
	// Build <select> element.
	$html = '<select id="myplugin_field_2" name="myplugin_field_2">';

	foreach ( $options as $value => $text )
	{
		$html .= '<option value="'. $value .'"';

		// We make sure the current options selected.
		if ( $value == $current ) $html .= ' selected="selected"';

		$html .= '>'. $text .'</option>';
	}
	
	$html .= '</select>';

	echo( $html );	
}

/** Field 3 Input **/
function myplugin_field_3_input() {

	// Output the form input, with the current setting as the value.
	echo( '<input type="text" name="myplugin_field_3" id="myplugin_field_3" value="'. get_option( 'myplugin_field_3' ) .'" />' );	
}

?>