WPC — Settings for Tell My Role plugin.

tmr-settings.php

<?php
/**
 * Settings Init.
 *
 * Initialize settings for the plugin.
 *
 * @since 1.0.0
 */
function tmr_settings_init() {
	// Register a new setting for `general` page.
	register_setting( 'general', 'tmr_setting' );

	// Register a new section in the `general` page.
	add_settings_section(
		'tmr_settings_section', // Section ID.
		'Tell My Role Settings', // Section Title.
		'tmr_settings_section_callback', // Section callback function.
		'general' // Slug of the admin page.
	);

	// Register a new field in the `tmr_settings_section` section, inside the `general` page.
	add_settings_field(
		'tmr_setting_field', // Setting ID.
		'Setting Title', // Setting Title
		'tmr_settings_field_callback', // Setting callback function.
		'general', // Slug of the admin page.
		'tmr_settings_section' // Setting section ID.
	);
}

// Register tmr_settings_init to the admin_init action hook.
add_action( 'admin_init', 'tmr_settings_init' );

/**
 * Section Content Callback.
 */
function tmr_settings_section_callback() {
	echo '<p>Plugin Settings Section</p>';
}

/**
 * Setting Field Content Callback.
 */
function tmr_settings_field_callback() {
	// Get the value of the setting we've registered with register_setting().
	$setting = get_option( 'tmr_setting' );

	// Output the field.
	?>
	<input type="text" name="tmr_setting" value="<?php isset( $setting ) ? esc_attr( $setting ) : ''; ?>">
	<?php
}