Click the "Review" tab on the top toolbar.
Click "Final Showing Markup" so that the document shows your edits.
Click "Track Changes" in the Tracking section.
Make changes, including deletions and insertions, in the document.
Click "Balloons" in the Tracking section and choose "Show Revisions in Balloons" if you want changes to be shown in balloons on the right side of the text. Alternatively, choose "Show All Revisions Inline" from the "Balloons" button if you want changes to be shown in the regular text.