plugin_admin_page_function.php

<?php
add_action('admin_menu', 'plugin_admin_add_page');
function plugin_admin_add_page() {
  add_options_page('Custom Plugin Page', 'Custom Plugin Options Page', 'manage_options', 'page_slug', 'plugin_options_page'); //settings menu page
}

function plugin_options_page() {
    //HTML and PHP for Plugin Admin Page
    echo "<h2>The Custom Plugin Options Page</h2>";
}
?>