While composing a new email, click on the paperclip with "attach" underneath it. Browse to the file on your hard disk. Select it and click on the "attach" button. The name and size of the attachment will then be shown in the attachments field of your email, which is not shown if the email has no attachments.
Befor you send out something as important as a CV, as an attachment - it pays to cross-check that the attachment will be acceptable to the other end - and to warn them that you're sending an attachment (for security purposes).
Most people can accept Word attachments, so it shouldn't be a problem - but check anyway, in case there are any other restrictions.