You have to add your email address to the phone. ( open settings, mail /calendar /contacts, add account). Add the email address and password to your phone. Then you can open email and send email from your contacts list.
wifi or cellular connection is required.
please look at the Apple manual for further assistance in all functions. iPhone - Apple Support
IF you are having a particular problem sending email, please post a more specific question/problem so we can suggest a solution.
