This article is a general overview of discussions, if you want to learn more about timestamp comments or annotations please visit these articles:
Annotations
Timestamp Comments

Collaboration is an important part of the creative process. With Discussions, collaborating on visual assets is a breeze.

Discussions enable you to comment on assets, tag team members, and share feedback instantly. You can also keep track of comments on multiple versions of the asset all in one place. Simply click on the asset and navigate to the Comments section. This is the first option in the sidebar menu. Type your thoughts and hit Post! Your comments are now visible to your teammates.

If you want to tag particular members of your team, type @ and the person's name.

You also have the option of editing and deleting comments, or marking them as resolved. To do so, hover your mouse over your comment until you see ellipses (three dots) appear next to it. Click on the ellipses and select Edit, Delete comment, or Mark as resolved.

When you mark a comment as resolved, it will disappear from the chat by default. To revisit the comment, change the option on the drop-down menu from "Unresolved only" to "Show all comments."

If you want to comment on a different version of the asset, simply navigate to the Versions option that is right underneath Comments in the sidebar menu. Click on your desired version and navigate back to Comments and you're good to go! The little "v1" or "v2" next to the comment tells you which version the comment is associated with.