Open up a chat with others inside of a Google Doc, Sheets, Slide.
Google Docs, Sheets, and Slides has a great feature built in that will allow the user to open up a chat with another user. This is available by selecting the gray circle to the right of the user profile picture. Once selected the chat opens and you can send the user a message. Please note that this chat can not be deleted, so whatever you type you can not take back.
This is especially helpful for communicating with others quickly and easily without having to comment within the file itself.
Embedded below is a GIF followed by a 51 second YouTube tutorial.