There are two options in Word for group work: you save a document to a shared area (storage area or shared folder on a network) and Share Document so that other users can change its contents; then, with Track Changes, you will be able to view the changes made by other users once those have been saved, and you can accept or refuse particular changes by particular users, and even merge all the changes into the original document or into a new document. If a conflict exists between any of the changes (for example, if two users edit the same cell), you can indicate which change you want to keep.

With co-authoring, you save the document to an online storage area (OneDrive, or Office 365 SharePoint) and then share the workbook with other users; when you and other users work on the workbook, your will see the changes made by each user in real time.