Youtube API module: Post videos to Youtube
Create a custom module, in mymodule.module use hook_node_update

function mymodule_node_update($node) {

  if (isset($node-&gt;field_checkbox[LANGUAGE_NONE][0]['value'])) { 
  // If field checkbox is set (not empty), then...

     // youtube api code goes here. 

  }

}



  The Youtube API module seems to be the appropriate module to do this,
  But I really have no idea of how to use this module.


According to the Youtube API module project page:


  This module is an API module, meaning that it in itself doesn't do
  anything


Therefore, all this module does is install libraries that you need in order to interact with the Youtube API, nothing more.

You need to read the Youtube API documentation from https://developers.google.com/youtube/documentation/
and learn how to code for youtube api.