The "Related pages" widget relies on pages meta-keywords to create a list of pages that would be related to the very page you are on. It brings a list of pages using the teaser image and teaser text from those pages.
3 parameters are asked:
1) Relevance: this the minimum number of keywords a page should have to be considered "related" to the current page. obviously the more the more relevant the relation will be.
2) Max results: How many related pages you want to show.
3) Use the teaser image or not for the list.