This plugin works in the same way with Joomla Groups plugin. The only difference is that it will assign subscribers of a subscription plan to selected K2 Group when subscription become active and remove them from the K2 Group when subscription is expired
This is useful if you use K2 extension on your site and want to give subscribers some special permission on K2
To use this plugin, go to Extensions -> Plugins, find and publish OS Membership - K2 Groups plugin plugin. Then edit the subscription plan, look at K2 Groups Settings tab, make necessary settings to get it works as you expected.