Google Docs comments can be used for various purposes, including leaving reminders for oneself, chatting asynchronously with others, and assigning tasks to team members. To add a comment in Google Docs, highlight the text or image you want to comment on, click the Add comment icon, type your comment, and then click Comment. Comments can be edited by clicking the More options icon, deleting comments by clicking Delete, viewing comments by clicking Open comment history, and printing documents with comments by downloading them as Microsoft Word files. Comments can also be replied to, reacted to, assigned to team members, shared with others, hidden, or resolved. Additionally, Google Docs has automation capabilities through Zapier integrations to notify others when they've been tagged in a comment or given access to a document.