The Review dropdown lets you manage your spreadsheet comments.
Comment – Adds a comment to the selected cell or cell range.
Edit Comment – Edits a comment in the selected cell or cell range.
Delete Comment – Removes a comment from the selected cell or cell range.
Previous Comment – Jumps to the previous comment in the spreadsheet.
Next Comment – Jumps to the next comment in the spreadsheet.
Protect Sheet... – Opens the protect sheet dialog, which allows you to apply editing restrictions. Note that restrictions are applied to the current sheet only and protect passwords are not recoverable!