Ensure your computer is connected to the internet before adding your email account.
In Mozilla Thunderbird, go to the "Tools" menu, then select "Account Settings"
Select "Account Actions" and then click "Add Mail Account"
Enter your name, email address and password and click "Continue", Thunderbird will try to connect to the server, click the "Stop" button several times until the Edit Config screen is shown as below:
Enter your account "User Name" and set the Incoming account type to be POP, Port 110 and None on the final menu.
Set the "Outgoing" server to the smtp server for your ISP
Click "Re-rest Configuration" and then "Create Account"
If you are shown a warning screen, click "I understand the risks" and then "Create Account"
Your "Account Settings" window will now list your new account.
Click "OK" on the main Account settings window.
Your new email account is setup and ready to use.