People can suggest edits on a Google Doc when they have Comment or Edit access on a document. Suggested edits are Google Docs version of track changes. If you upload and convert a Microsoft Word document with track changes to Google Docs the track changes will become suggested edits.
Step 1 - You must be in 'Suggesting mode' to make suggestions. To do this, click the 'View' menu and click 'Mode' then 'Suggesting'.
You can also access it from the pencil icon on the right of the toolbar.
Or from the 'Suggest edits' button to the right of the page.
Step 2 - You can now make edits, as you do this you will see a green box around the new content you type.
Step 3 - These suggestions can then be approved or declined with the tick or cross icon.