Select Account Settings
Select Add Mail Account
Enter the login details of your Email account
Click Continue and allow Thunderbird to find your account settings. Press Done
Thunderbird does not like sites which reside on shared servers and presents a security warning. There is no real security issue here, so go ahead and click Confirm Security Exception
Now go back to the account settings and change the email address to be your personal one, rather than the one used for login. You might login with firstname.lastname@example.org but use email@example.com to answer emails.