90% of the plugins you use, will have some options in the dashboard. It makes sense to allow users some setting options, to tailor the functionality of a plugin, according to their preference. This can increase the usability of a plugin.

Create an Options Page for a Plugin under Settings Menu

To create a sub-menu for your plugin in the dashboard ‘Settings’ menu, you should use the Settings API provided by WordPress. Using this API, you can register a new options page, with fields for settings. Additionally, you can add settings to an existing options page.

Register Settings For a Plugin

For settings belonging to a particular plugin, you need to register the settings in a single group, with a unique id. For example, you need to write something like the following:

function myplugin_register_settings() {
   add_option( 'myplugin_option_name', 'This is my option value.');
   register_setting( 'myplugin_options_group', 'myplugin_option_name', 'myplugin_callback' );
}
add_action( 'admin_init', 'myplugin_register_settings' );

Here, all the settings fields for the plugin will be grouped under myplugin_options_group. In an options page, this id will be used to display the fields.