Enter the details of your message in the top form.
Enter your email message into the center text box.
You can drag/drop any files you wish to attach to the box on the right. Alternatively you can click Attach a File in the top of the pane to bring up a folder browser menu.
Click the Send button to send the email, alternatively you can click Save to come back to it later.
You can save email addresses to the Address Book to make filling in the To field easier.