The Topic Editor is used to author free format Topics. Topics can contain any content you would like to include in the generated documentation; e.g. tutorials, conceptual background, procedures etc.
If your project contains more than one Build Profile you may want to choose which Build Profile to use when editing and Previewing in the Topic Editor, so that your authoring experience matches that of a specific Build Profile (e.g. the chosen Template and in Preview the Build Flags and other content filters). For instance if your project contains Build Profiles that use different templates or use different Build Flags rules you might want to check how your content looks in both output types.
Click the wrench icon on the Topic Edit window Tab Header to show the WYSIWYG Profile selector and select the Build Profile you want to use for Edit and Preview.