When you are in Messages view and typing a message, you will notice a plus sign (+, turquoise circle and arrow in image below) to the left side of the message box.
If you click on this icon, a variety of actions are displayed.
As soon as you click in the message box, these action fields will open automatically. They will stay open even if you move to another message. They will close when you refresh the page.
Let's explore these action items.
Add Image, Add Video (beta), Add Attachment, Add URL, Add Template, Add Merge Fields (same article for all these items)