• Here is a demo plugin for more clarification. To install the plugin, please download from here. 
• Create a plugin with a unique folder name.
• Create a index.php file at the root directory of plugin folder.
• Add meta data to index.php file as like below:

<?php

//Prevent direct access
defined('PLUGINPATH') or exit('No direct script access allowed');

/*
Plugin Name: Your Plugin Name
Plugin URL: https://codecanyon.net/item/your_item
Description: Your plugin description
Version: 1.0
Requires at least: 2.8
Author: Author name
Author URL: https://codecanyon.net/user/author_url
*/                 

Note: The meta data is needed to add only in index.php file.

• This is now indexed in RISE. Go to Settings > Plugins. There you can install and activate this plugin.
• You can also create a .zip file with your plugin folder and install it from Settings > Plugins.