Add attach programatically

Hi,
Im a newbie WP developer and need to programatically add an attachment to my custom post. I have look your plugin and find the save_metadata method in Attachments class.
Can you provide an example of the correct way to call the method and populate the $attachments_meta parameter?
Hope that my question are clear, Im not a good english spoker 🙂
regards,
ale.-

https://wordpress.org/plugins/attachments/