I'm not exactly certain what the issue is. You do not sign in to Thunderbird, it is just an email clinet program. Do you mean you have created mail accounts in Thunderbird, but your password is being refused? do you get an error message? If yes, what error message...word for word?

re :I already have email and password Have you created a mail account in Thunderbird for that email address? If yes: If it is an IMAP mail account, have you subscribed to see folders? If no: Right click on mail account and select 'Subscribe' to see a list of folders you can choose to subscribe to see.

If you mean how do I create a mail account for my email address:

logon to webmail account using a browser. Select to use POP or IMAP mail forwarding. The type you select must be the same one you select to use in Thunderbird.

In Thunderbird File > New > Existing Mail account or Menu icon > New Messages > Existing Mail account

Enter name enter full email address Enter password select to remember pasword click on 'Continue' button

Thunderbird will try to locate server setting configuration. Check that the correct type: POP or IMAP has been chosen If details look correct click on 'Done' to create mail account

if you need to modify anything, click on 'Manual config' button. Make any changes you require. Use the 'Re-Test' button to check settings. click on 'Done' to create mail account

Thanks!