Thunderbird is attempting to set your account up - server names, ports, security, etc. You don't need to enter your email account password yet. You can wait until the account is established and the, when you check mail, you will be prompted for the password. If you're unsure of email account settings, check with your email provider for the specifics. Another way people get that info that is often successful is to do a websearch, entering name of email provider (e.g., AOL, GMAIL, etc.) and the two words email setting