Similar to Ticket Detail, Comments tab section is divided into several parts. The top most part contains source icon, task Subject, link to parent ticket, total time spent (Note: displayed only if comment timer is enabled), Created, Updated (User and time) and Stage. Below those is the Description.
Task Description can be edited (this option is controlled by system permission). If you have permission to edit the description there is an Edit link in lower right corner. This link opens a popup with a text box containing the current task description.
Below this part is the comment box displayed where you can add comments for the task. Below the comment box, existing comments are displayed. Functions are similar to comment section of Ticket Detail, see section Ticket Comments.
Note that for a task all comments should be set as Public. A task has no Requester (End User) as recipient of Public comments, so in fact there is no difference if comment is set Internal.