Need help moving to the next step with my plugin

Hi there. Thanks in advance to everyone who helps out here!

I have decided to create my first WordPress plugin and everything seems to be pretty straight forward and the documentation is great. However, I am stuck. ??

Below is my main plugin file code.

<?php
/*
Plugin Name: The Web Design Toolbox
Plugin URI: https://www.thewebdesigntoolbox.com
Description: A WordPress plugin that brings you many tools to easily create web elements. Our goal is to be a one stop solution for all your web design tools.
Version: 1.0
Author: Jonathon Hammond
Author URI: https://www.yourwebdesigntoolbox.com
License: GPL2
*/

/*
Copyright 2013 Your Web-Design Toolbox (email: [email protected])
*/
?><?php

// some definition we will use
define( 'twtb_PUGIN_NAME', 'The Web Design Tool Box');
define( 'twtb_PLUGIN_DIRECTORY', 'the-web-design-toolbox');
define( 'twtb_CURRENT_VERSION', '1.0' );
define( 'twtb_CURRENT_BUILD', '1' );
define( 'twtb_LOGPATH', str_replace('\\', '/', WP_CONTENT_DIR).'/twtb-logs/');
define( 'twtb_DEBUG', false);		# never use debug mode on productive systems
// i18n plugin domain for language files
define( 'EMU2_I18N_DOMAIN', 'twtb' );

// how to handle log files, don't load them if you don't log
require_once('twtb_logfilehandling.php');

// load language files
function twtb_set_lang_file() {
	# set the language file
	$currentLocale = get_locale();
	if(!empty($currentLocale)) {
		$moFile = dirname(__FILE__) . "/lang/" . $currentLocale . ".mo";
		if (@file_exists($moFile) && is_readable($moFile)) {
			load_textdomain(EMU2_I18N_DOMAIN, $moFile);
		}

	}
}
twtb_set_lang_file();

// create custom plugin settings menu
add_action( 'admin_menu', 'twtb_create_menu' );

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

register_activation_hook(__FILE__, 'twtb_activate');
register_deactivation_hook(__FILE__, 'twtb_deactivate');
register_uninstall_hook(__FILE__, 'twtb_uninstall');

// activating the default values
function twtb_activate() {
	add_option('twtb_option_3', 'any_value');
}

// deactivating
function twtb_deactivate() {
	// needed for proper deletion of every option
	delete_option('twtb_option_3');
}

// uninstalling
function twtb_uninstall() {
	# delete all data stored
	delete_option('twtb_option_3');
	// delete log files and folder only if needed
	if (function_exists('twtb_deleteLogFolder')) twtb_deleteLogFolder();
}

function twtb_create_menu() {

	// create new top-level menu
	add_menu_page(
	__('Design Toolbox', EMU2_I18N_DOMAIN),
	__('Design Toolbox', EMU2_I18N_DOMAIN),
	0,
	twtb_PLUGIN_DIRECTORY.'/twtb_settings_page.php',
	'',
	plugins_url('/images/icon.png', __FILE__));

	add_submenu_page(
	twtb_PLUGIN_DIRECTORY.'/twtb_settings_page.php',
	__("Element Generator", EMU2_I18N_DOMAIN),
	__("Element Generator", EMU2_I18N_DOMAIN),
	0,
	twtb_PLUGIN_DIRECTORY.'/twtb_settings_page.php'
	);

	add_submenu_page(
	twtb_PLUGIN_DIRECTORY.'/twtb_settings_page.php',
	__("Support", EMU2_I18N_DOMAIN),
	__("Support", EMU2_I18N_DOMAIN),
	9,
	twtb_PLUGIN_DIRECTORY.'/twtb_settings_page2.php'
	);

}

function twtb_register_settings() {
	//register settings
	register_setting( 'twtb-settings-group', 'new_option_name' );
	register_setting( 'twtb-settings-group', 'some_other_option' );
	register_setting( 'twtb-settings-group', 'option_etc' );
}

// check if debug is activated
function twtb_debug() {
	# only run debug on localhost
	if ($_SERVER["HTTP_HOST"]=="localhost" && defined('EPS_DEBUG') && EPS_DEBUG==true) return true;
}
?>

<?php
    add_action( 'admin_enqueue_scripts', 'safely_add_stylesheet_to_admin' );
    /**
     * Add stylesheet to the page
     */
    function safely_add_stylesheet_to_admin() {
        wp_enqueue_style( 'prefix-style', plugins_url('style.css', __FILE__) );
    }
?>

And here is a sidebar.php that I pulled into one of my menu items for the plugin

<?php

?>
<ul>
	<li><h3>The Toolbox</h3></li>
	<li><a href="#">CSS Button Generator</a></li>
	<li><a href="#">CSS Transition</a></li>
	<li><a href="#">CSS Gradient</a></li>
	<li><a href="#">DIV Style</a></li>
	<li><a href="#">Paralax</a></li>
	<li><a href="#">More Tools</a></li>
</ul>
<?php

?>

I am wanting to create a PHP file for each feature here… So for example create the following……

button_gen.php
css_gradient.php
etc, etc…

I tried to link to the file with traditional HTML but no luck.

Am I taking the wrong approach here?