The Application Help (OOo OnlineHelp) is displayed in the Help Viewer window.
The Help Viewer displays HTML 3.2 pages, using the OOo Writer/Web module. This has the side effect that you can open an HTML document in Writer/Web, change the zoom factor, then open the Application Help to see the same zoom factor. This may be called a bug or a feature.
The Help Viewer opens when a user presses F1, or activates the Help button in a dialog box, or chooses the menu Help - Contents. The shown Help page can be different according to Help context (for example, the Writer or Calc module).
The Help Viewer offers some tab pages at the left side of its window, and the current help page on the right side.
Tab pages at the left side: