The Research tool in Google Docs is an interesting feature which harnesses the power of Google search by allowing you to perform research tasks from within Google Docs.

You can select the Research Tool from Tools menu or use the short cut Ctrl+Alt+Shift+I.

The Research results are displayed in the form of a sidebar with a Google search box displayed on the top. The search results will contain various information like images, scholarly articles, quotes etc. as shown in the image below. The Filter drop-down allows you to limit the search to one of the categories.

You can now select and insert any of the displayed results into your document. Most of the results have a Cite button as well, which will create a footnote citation.

Alternatively, you can right-click on a word or phrase in the document and select 'Research ...' to see the search results in the Research sidebar.

Another feature which you may find very useful is the Advanced filter option "Filter image results by usage rights:" which filters the search results to content that you can use, share, or modify something you find online.