These are word processing documents which are edited much like any other word processing documents.
You can save these documents to your Google drive and share them with other people for a group-created and group-edited document.
Open a new document and it looks like a typical word processing program:
A document can be typed as per any other basic word processing program. All of your work is automatically saved and updated from device to device every time you open the document.
Making a comment with a documents is easy! Open the document and highlight the part you want to make a comment on. Go to Insert and choose Comment. A comment box will appear where you can make your comment. It includes your name so group commenting is possible.
Here is a sample: