Before proceeding, you should take a look at the article: Viewing a Task
You can add a message to the Chat via the Message box at the bottom of the page.
Hint! The Chat channel can be used to keep your own notes on a task or to communicate with others.
To tag someone, simply type @ - this will trigger a small menu to automatically display, showing a list of users who you can tag. The list only shows the first 5 results. You should start typing the first few characters of their name to find the user you want, if they don’t immediately appear.
You can add a reply to a specific Comment. There is a ‘Reply’ action by each comment, or alternatively - if replies exist already - the user can open the replies chain and type directly into the Replies message box which opens. To ‘go back’ to entering regular Comments, you need to hit ‘Hide replies’. When hovering your cursor over your comment, a pencil icon will appear. When clicked, you can edit your comment or reply. You cannot delete the comment entirely.
You will receive a notification when a new chat is sent to you. For more information, please view the article: Tasks Notifications