Trope: The backbone of this site. A description of a recurring pattern in fiction which should come with a list of examples. Example: Sealed Evil in a Can.
Work: A description of a piece of fiction in which tropes may occur, containing a list of the tropes that exist in that piece of fiction. This page type enables reviews, the YMMV tab, and several other features. Additionally, if the Recap page for an individual episode of a series has its own reviews, it will need this page type for tech reasons. Example: Tomorrow Never Dies.
A creator or person: A page about some real-life entity associated with the creation of works (like an author, an actor or a production studio). Example: David Tennant.
Index: A page whose main function is to list other pages. If you want a page to show up in the center of the little blue index bars at the bottom of other pages, it needs to have this type. If the page is doing the indexing job in addition to being about a work or one of the other pages types, check-off the "doing indexing" box. Example: Espionage Tropes.