The knowledge base lets you author help articles, organize them into categories, and pick them into ticket replies. Manage it under the help desk's Knowledge base area.
Articles have a status (draft, published, archived) and a visibility (public or internal):
Published public articles are searchable by customers on the portal (deflecting tickets before they're created) and by agents composing replies (so they can drop in an accurate answer instantly). Investing in a handful of great articles for your most common questions pays off quickly.