Press the button with the icon on the lower right of your screen.
This button summarizes whatever text you have selected on a page, or the whole page if nothing is selected. It also works with PDFs, YouTube videos, Google Docs and Google Slide decks, so you can get a summary of what you're looking at quickly.
This button is called a Tool Button, and it runs something called a Tool. Tool Buttons give you 1-click access to help on every web page, and you can customize them to fit your needs.
Here a some other pages to try your new summarizing superpower on: