There are a few ways to add a comment on an item in your project (such as a task, milestone, file, notebook or link).

On the details page for an individual item

Click on the comment box at the bottom of page:

In the quick view overlay of an item

Click on the comment box under the item details:

Formatting and other options

When you click to add a comment using any of the methods above, you'll see the message editor screen:

You can use the formatting toolbar to style the text in your comment and add images or links. 

If you use the '@name' mention option within the comment, that person will automatically be added to the notify option:

Under the editor, you can select who to notify of your comment, you can attach files, and if there isn't already a privacy setting on the item you're commenting on, you can choose who the comment should be
private to.

Comment link

If you have lots of comments and want to link to a comment directly, you can do so by using the Permalink feature. By clicking the link button on the left you will get a direct link to the comment that can be shared or linked to on a Notebook or Message

Editing Comments

Administrators can delete comments created by anyone. Everyone else can delete their own comments within 15 minutes of adding them.