saving my emails, (archive)?

I just realized that updates to Thunderbird over the last year or so has totally changed the location of my emails (I used to know where they all are - now I can find no evidence of them). I have many "folders" in my account and I want to save them (like I used to be able to do). Now I can't even find them. I started reading and it appears I need to "archive" them. The help says to somehow select the files (I want to select whole folders) and then hit the Archive button - or hit A on the keyboard. To start I selected a single folder and since I can find no evidence of a "archive button", I hit A. If anything happened I can't find it. Is archive what I need? I can't even find any definition of archive. The help assumes I have an "archive button" -- can someone please tell me where to find it? I very much need these files. Thanks to anyone who can give me some help. Rob