To insert the text in your document that you want to place as a comment.
Select the desired text.
From the Common
tab, select Comment 
.
You can also use the shortcut ALT+M (Refer to list of shortcuts).
This command inserts comment tags in your document. They are: <!-- and -->.
Comment tags are an integral part of the HTML document, but they are not displayed buy the browser. They are used to enter information concerning the design of the Web page and to insert key words in the document so that search engines can take them into account.
To insert the text in your document that you want to place as a comment.
Select the desired text.
From the Common
tab, select Comment .
You can also use the shortcut ALT+M (Refer to list of shortcuts).
The selected text will be inserted between the tags <!-- and -->.