Automatic Installation of Core Plugins
Plugins shipped with JomSocial 4 are automatically installed.
Every time you install JomSocial component, all available plugins will be installed automatically as well. Not all plugins will be published automatically though. You will neet to publish plugins manually using Joomla plugin manager.
Manual Installation of Extra Plugins
Extra plugins are shipped separately and hence they must be installed manually.
To do so, download the plugin to your computer and install it the same way as you would install any other Joomla extension.