Your professor or TA will receive a link to the doc and a notification telling them that you have shared your doc with them. When they open the doc you will notice that their user name will appear in the top right corner of the screen. You are now collaborating in Google Docs.
Your professor or TA can now help you revise your doc in real time. Clicking the blue box in the upper right hand corner of the screen will allow you to chat with them and ask questions as you move through the doc. Your editor can also add comments to your doc without actually rewriting the text. Highlighting a passage and then selecting 'Insert > Comment' will allow them to make a note about that section to the right of the page.
Your professor or TA’s cursor will be visible as they move through the doc to show where there are currently reviewing or editing. Their cursor will appear in the color corresponding to the box next to their display name in the chat box. When they highlight a passage you will also be able to see their highlighted section in their color. As more people are invited to collaborate on the doc they will have different colors assigned to them so that you can tell who made each comment or revision.