Well lets start as the beginning. Have you actually received mail on the account in Thunderbird? Having only an inbox and a trash is fairly common of a non working IMAP mail account.

Is your account set up as POP? Pop mail accounts only ever see mail in the inbox. It is inherent in the account protocol for POP where it is referred to as the "mail drop"

Note: Pressing F10 will make a menu bar appear if it is not already visible, right clicking the toolbar will offer a menu to turn it on permanently.

I did receive Inbox emails. It has been years since I have had to set up POP emails. Which do I need to set to POP--Thunderbird or Outlook?

If you want to see all the folders, add the account as IMAP. If it's already IMAP (Server Type in Account Settings, Server Settings), and you don't see the folders, right-click the account in the Folder Pane, Subscribe, Refresh, check the boxes for the desired folders.

If it's currently POP, to change to IMAP you have to re-add the account as IMAP:

http://kb.mozillazine.org/Convert_a_POP_account_to_a_IMAP_account

For IMAP, use outlook.office365.com on 993, SSL/TLS, and smtp.office365.com on 587, STARTTLS; authentication = normal password, User Name = email address.

Thanks! I see all of my folders.

Next question. Now that I can see them and have Thunderbird setup to download to my computer, how do I download old emails? Thunderbird offers to let me download new/unread emails but I don't see a way to download emails that I have read and saved in various folders.

If the account is IMAP, in the Sync. & Storage section of Account Settings, there is 'Sync. all messages locally regardless of age' button. If that's already selected, selecting a folder should sync with all messages on the server. Right-click a folder, Properties, Repair Folder, to force the download of all messages on the server.