Word keeps track of all the changes being made in the file and displays a bracket adjacent to areas to which any other people working in the file have applied changed. When you save the document, Word lets everyone else know that an update of the file is available, and when they save their versions of the file, Word synchronizes all the changes and highlights added text so that each person can see what their co-authors have changed.
Open a shared document and make the desired changes.
When a co-author makes changes in the document, a bracket shows where the changes have been made along with the name of the individual who made the change.
When the other author saves ...