wp-create-settings-section.php

<?php

add_action('admin_init', 'add_options_section');

function add_options_section() {
  add_settins_section(
    'section_name',
    'Section Title',
    'section_callback',
    'reading'
  );

  add_settings_field(
    'field_name',
    'Field Label',
    'field_callback',
    'reading',
    'section_name'
  );

  register_setting('reading', 'option_name', 'strip_tags');
}

function section_callback() {
  echo 'Some message before options fields';
}

function field_callback() {
  $option = get_option('option_name');
  ?>
    <input name='option_name' value='<?= $option ?>'>
  <?php
}