Dynamic Help
If you are working through a task and encounter a part of the interface that you do not understand, you can summon context-sensitive help.
By default, this will display the Help view opened to Related Topics page and give you some specific information about the view/editor/dialog you are using, and possibly some links to topics for further help.
Context-sensitive help can be accessed by bringing focus to the interface part in question by clicking on it or using the Tab key, and then pressing F1 (Shift+F1 on GTK+, and Help on the Mac).
Alternatively, in dialogs you can achieve the same result by pressing the Dynamic help button in the dialog's button bar.