User Synchronization

I have followed through all the steps to setup the plugin, but nothing seems to happen to sync my users that are added to the main site when I select the Sync Users. I see no user information added to the sub-sites.

I assume from the limited description, that this is to sync users from the main site to sub-sites?

Also, is this to happen automatically after it's all setup, or does someone need to run the "user sync" each time to initiate the transfer of the users to all the sites?