The two main features of the Reviewing Toolbar (RT) are the "Comment" and "Track Change" feature. With these, you can make comments and changes to a document, and then give the reader the option of accepting or rejecting them.
Using the RT is the most economical way to edit a document. If it is does not appear by default you can turn it on.
There are three possible ways how to do that:
1. View>Toolbar>Reviewing
2. Right click on any Toolbar> Reviewing
3. Double click on TRK in the Status Bar