If there is a particular mail you received and would like to send it to someone else, click on the 'Forward' button.
You will be taken to ‘Write mail’ where you just need to add the email ID of your friend(s).
The original mail gets attached to your outgoing mail.
The subject line shows Fwd: (the subject of the original mail). Inside the mail, a message gets added - Note: Forwarded message attached.