As part of learning the interface, I’m going to explain what each button does.
Get Mail – checks the email server for new messages and sends any messages you have waiting to go out.
Write – opens a blank email.
Address Book – opens up your address book.
Reply – opens an existing email and allows you to reply to the sender.
Reply All – opens an existing email and allows to you reply to the sender and all the other recipients.
Forward – opens an existing email and allows you to send it to someone else.
Delete – throws an existing email away.
File – allows you to move an email to another folder.
Junk – labels a message as “junk mail”. If your Junk Mail Controls are setup, it will also move the “junk” message to the Junk folder.
Print – allows you to print an email.
Stop – stops Thunderbird from contacting a server.
Posted by Slushman 
The default setting for Thunderbird to check for new mail is 10 minutes. Some people prefer to get it more often than that (I know I do). To change this setting, go to Tools > Account Settings. This will open the Account Settings options. From here, click on the “Server Settings” option listed under the email account for which you want to change the time. The second section, labeled Server Settings, has the setting for “Check for new messages every _ minutes”. Change that number to whatever you want and presto!
The unofficial how-to blog for Thunderbird 