This script does not actually authenticate a user between different portals. It instead provides a method, with some assistance from a middle-script, to register a user within a different system. For your specific case, when a user registered on your WordPress site, the information could be transmitted off to your middle-script which stores the user information on the Joomla site, such that the user does not actually have to register for both sites and instead will have their user information already available in the other site.

Let me admit I am not too much a techy guy but still understand a bit of it. Just one question….. Is it possible to use this as a single sign-on between WordPress & Joomla? If yes… would you be kindly detail the steps required to do so?

This plugin is not designed to work specifically with any particular external system. Instead it provides a method to connect to an external script which can then integrate the WordPress/BuddyPress sign up information with another system such as a forum board, e-commerce system, newsletter system, etc… In order to work the transaction URL must point to a script which interprets the information being sent by this plugin and then performing the respective actions to integrate this information with your external system. In short, this plugin is designed to facilitate the ability as opposed to providing a universal solution.

Currently this plugin does not monitor for changes to the user account, however it has been noted for a future release. This of course would only be able to monitor changes on either the WordPress or BuddyPress profile side.

To answer your second question this plugin does not require BuddyPress and was actually built specifically for the WordPress platform. It has been configured however to also work with sites running the BuddyPress plugin. So in short, will work just fine in either circumstance.