The Summary portlet functions differently depending on which kind of page it is added to, but in general it displays an overview of the community that it is placed in. The Summary portlet is a part of the Social Networking portlet package in 6.x; in versions prior to 6.x it is a part of the World of Liferay portlet package.
When placed on a page within a community or organization, the Summary portlet provides users the ability to join or leave the community or organization.
When placed on a user's personal page, the Summary portlet will display an overview of the user's profile. The Summary portlet also provides the ability to add the respected user as a friend.