The Manage Group dialog allows users to create and manage groups of tables in a specific schema/catalog. It can be invoked by pressing the filter button in the Relation Tab and selecting "Show Group -> Create/Manage Groups" menu item.
Groups can be created by right clicking in the Group Hierarchy tree on the right pane. To add tables to a group you can select one or more tables in the table list on the right pane, and drag the selected tables on the group.
To view the tables in the group, you can set the filter mode in Relation Tab to be "Show Group" and select the named group in the sub menu.