There are two ways to search for Help items; in the Help panel and in the gallery of Help items. Here is what a search looks like from the Help panel:
When conducted from within the Help panel, only Help items in the scope you are in will be searched, i.e., if you are in a document library, only help items related to a document library will be searched. To expand your search to the entire gallery of help items, click Search all help items…:
Clicking this link will open the gallery of help items in another window and will search all of the available help items for your query term.
Your query term will be searched across the Title, Media, Description, Viewer, Content Pack name, customization status, SharePoint scope, and app scope fields. Fields will be searched in real time.