The request is apparently for the text to be sent within the BODY of the email, and NOT as a separate attachment.
When using an email client (such as Outlook, Outlook Express, Windows Live Mail or Thunderbird) you choose whether to send the mail as 'plain text' or as 'rich text' (which uses the HTML format).
Plain text simply sends the words without any formatting (such as bold, italic or underlined text, or allowing the use of different fonts and sizes). Rich text (HTML) allows all of those things to be included.
If your brother is using a proper email client (such as Outlook Express, etc) he should create a new mail and then click on 'Format' to check that 'Rich text (HTML)' is selected. If he's only using a web-based service that option might not be available. In which case he'll be stuck with either using plain text or sending an attachment. (His choice will depend upon whether or not the formatting of his work is particularly important and, of course, upon whether the recipient's email service accepts attachments).
Chris