Contextual menus
A contextual menu is a menu that appears under your pointer when you right-click or Control-click certain parts of the interface. OmniOutliner has contextual menus for rows, columns, selected text, the sections list, and the styles palette. Just right-click or Control-click on one of these objects and a menu will appear, containing commands relevant to what you clicked. The commands are just convenient analogs for existing menu commands and inspector controls, so if you ignore the contextual menus completely you won't be missing anything.