If this is the first time you launched Thunderbird, it asks you whether you would like a new email address. Click Skip this and use my existing email and proceed to step 4.
Go to the File menu and select New, Existing Mail Account....
Enter your name (), email address () and your password. Make sure the Remember password checkbox is selected and click Continue.
Once the configuration has been automatically detected, make sure IMAP is selected and click Done.
To use your contacts from the server, click on the arrow next to "Address Books" and click the Connect button on each address book you would like to use.
To use your calendars from the server, click on the arrow next to "Calendars" and click the Connect button on each calendar you would like to use.
(Optional) If you want Thunderbird to sync all subfolders, go to the Account Settings menu and select Server Settings. In the Server Settings tab, click on the Advanced button. In the Advanced Account Settings window, uncheck the "Show only subscribed folders" checkbox. Click OK to save the changes.