You might want to compose a new mail, or reply to an existing mail. You can adjust who your message is going to by changing the list of email addresses in the ‘to’ field.
The ‘cc’ (carbon copy) field allows you to set who else will be sent a copy. The ‘bcc’ (blind carbon copy) field allows you to choose who else will be sent a copy without anyone else knowing that you’ve also included them.
You can also attach files, and change the formatting of your message.