The information you're looking for is found on the third page (Server Information) of the Account Wizard, which opens shortly after you run TB for the first time after installing it.
That's where you enter the names of your POP and SMTP
servers, but be sure to Un
check "Use Global Inbox (store mail in Local Folders)"
, which is checked by default.
If you've entered all the other required information correctly, you'll have a named account folder with an inbox, as well as the Local account. You can create as many subfolders in the Inbox and Sent folders as you like.
For an existing TB installation, even if you've used the default setting and left "Use Global Inbox (store mail in Local Folders)"
checked, you've still established a named account, even though it isn't displayed when using the Global (Local Folder) Inbox.
It's easy to switch to that named account in the Advanced Account Settings
window, accessed with the "Advanced" button at Tools > Account Settings... > Server Settings
. Then, after closing and reopening TB, any mail in the Local Folders can be moved to the named account simply by highlighting the messages, right-clicking on them, selecting "Move To", and choosing the desired folder.