Registering a New Options Page in WordPress

class-sample-plugin.php

<?php
if ( ! class_exists( 'Sample_Plugin' ) ) {
  class Sample_Plugin {
    var $text_domain = 'sample_plugin';
    var $options_page_slug = 'sample-options-page'; /* Because you will use this in a lot of places, we'll define it here */
    function __construct() {
      add_action( 'admin_menu', array( $this, 'admin_menu' ) );
    }
    
    function admin_menu() {
      add_options_page( 
        /* $page_title = */__( 'Sample Options Page', $this->text_domain ), /* Will be used as <title> element on page, only */
        /* $menu_title = */__( 'Sample Options', $this->text_domain ), /* Will appear as the name within the admin menu */
        /* $capability = */'manage_options', /* Be sure to choose a capability that makes sense for your plugin */
        /* $menu_slug  = */$this->options_page_slug, /* Make this unique, so that no other plugin/theme will clash with it */
        /* $callback   = */array( $this, 'do_options_page' ) /* This will actually output the HTML for the options page */
      );
    }
  }
}