In order to locate some of the tabs listed above, you may need to select the More icon at far right of the tabs to reveal a dropdown containing more options to select from.
While under any of these tabs, you can hover over any of the items in the list to reveal actions associated with that item (if any exist). For example, under the Files tab, hover your mouse over an attached file to download, share, rename, or view that file in the message thread. You may find some of these actions by clicking the More icon that appears at far right of the item.