TB probably looks in the default location for the wab file associated with your identity, It should work with no intervention.
For extensions, look under Tools/Add ons.

Update:

Here is the situation. I am setting up a new computer that does not have Outlook Express or any other previous email software. I am trying to move the settings and the email accounts and data from another computer.

I just managed to do one thing that will help. On the older computer, I just downloaded and installed Thunderbird and I loaded all the old email and settings into that copy of Thunderbird. So the question now is this. How do I move this information from the older computer to the new computer? What data files do I look for for moving from the older computer? I looked for an export option and I did not find one.

(The Extensions problem will be looked into after I fix this issue)

See "Move profile" here"
http://www.mozilla.org/support/thunderbird/profile
See"Mozbackup" here:
http://mozbackup.jasnapaka.com/