Content Queries are used in a wide variety of features, but put simply, they are used to pull data from somewhere on your site into a page. This data can be documents, images, pages, or list items. The Content Query uses a template to style that content after it is pulled into the page.
Content Query web parts are typically set up for you by Tyler Technologies. You won't need to worry about setting up the items involved with Content Queries, but it is helpful for you to understand how to identify one and how to make updates to the content it is showing.
Identifying a Content Query
There are a few ways to identify when a Content Query has been used on a page.
First, the web part will likely show a 'Content Query' title when viewing the page in edit mode.

You will also be
unable to edit any of the content in the web part. The content is being pulled into the page dynamically, so edits can't be made from the page it appears on.
Updating Content
So how do you make updates to the content in a Content Query? Updates need to be made where the content is coming from; the folder or list where the content lives.
Generally the Content Query is pulling from a folder or list in the same area of the site as the page the content is being loaded to.
From the page that is using the Content Query, click on the
Site Actions gear in the top right and
choose 'Site contents'.

On this page, look for a folder or list that has a name related to the content that the Content Query was loading. For example, if the query was loading in staff information, look for a list related to staff members.
If you do not find any folder or list relating to the query, try going to your site's home page, go the Site contents again, and look for the folder or list there.
Once you locate your list or folder, you can make the needed updates. For folders,
upload files or
delete files. For lists, make the needed changes to the
list items.
Note: Any updates you make to the documents or list items do not have a check in / publish process like the pages do. Any updates you make will start showing up on your site immediately.