I am trying to attach existing emails to a new email and found an answer but can not follow it along because I am not familar with some of the terms being used. The answer seems simple enough, it instructs to "You can drag and drop the messages to be attached from the thread pane of the main Thunderbird window to the header area of the compose window."

My problem is that I am not familiar with the terms being used and exactly where / what they are in Thunderbird. So, I am hoping that someone can tell me where I can find an explanation of the basics of Thunderbird. In particular I am looking to identify the "thread pane". Also am I correct in identifying the compose pane as the window that pops up when you click on write?