The Content Search Web Part and the other search-driven Web Parts display content based on search. Every time a user opens a page that has a Content Search Web Part or one of the other search-driven Web Parts on it, a query is sent to the search index, and search results are displayed automatically in the Web Part.
The different search-driven Web Parts have different default queries. For example, the Content Search Web Part shows recently changed items from the current page. As new content is discovered by search, an updated list of content is displayed each time a user views the page.
You can change the query in the Web Part to display content from other sites or lists.
To change the default query or build your own query
In the Web Part tool pane, under Search Criteria, click Change query.
In the Build your query window, change the default query or build your own query.
To define how many items to display in the Web Part
Under Number of items to show, enter how many items you want to display in the Web Part.